Our engine beds did get a little love back in 2016 when we put in the new Beta 35. Y’all remember that right… it was when Jon tried to smoosh me with our old 800lbs Yanmar. Check out that blog from 2016 to read about that fun day.
Anyways… We did a complete overhaul to our engine beds and I let Jon take over writing this one.
A Little Background History
Re-powering Prism, our HC33, has been one of the best upgrades to our boat over the last 10 years. It has given us more power, it weighs less and parts are very easily accessible as the base engine (a Kobota BV1505) is one of the most common small diesels in the world. It also lightened our drivetrain by nearly 400lbs, compared to the old Yanmar 3qm30.
When we first installed the the Beta in 2017 we did the re-power in the water in Colon Panama. After lots of careful measurements I gathered that I could reuse the old engine beds for the new Beta by just adding a 1’’ shim to the front engine mounts, no adjustment to the rear ones was needed. The old Yanmar engine mount brackets were offset by a fair amount, meaning that the front brackets were about an inch lower than the rear ones. The Beta had flat brackets, which meant that there was no drop between the brackets at all. Overall length of the engine and gearbox was similar to the Yanmar, including the output flange drop from the crankshaft and the TMC60 reduction ratio. This meant that a new prop shaft was not necessary and the swap should be fairly straight forward, and it was.
⬇️Blast from the past... photos from 2016⬇️
click photos to enlarge
The Original Engine Bed Design
The engine beds on the HC33 are arranged with four plateaus or table tops. These plateaus form bases which the engine mounts bolt to. The bases have a piece of 3/8’’ steel plate on top of wood that had been glassed over. The original setup had the Yanmar engine mounts tapped directly into these steel plates. This configuration works well, but there are a few shortcomings. First, any water that drips into the holes has a straight shot into the core of the engine beds, where there is no drain. If you are unlucky and enough water makes it into your boat where these become submerged, you would then have waterlogged engine beds. Eventually leading to rotten engine beds. We have seen this type of rot in a HC33 that we helped repair in Georgia, where this exact scenario happened. The next issue is if one of the bolts breaks off into that steel plate. If this happens, it is extraordinarily hard to remove the broken bolt as the engine is in the way. Our engine bed had two broken off bolts and the previous owners had simply rotated the engine mounts and drilled new holes. Thus leaving the broken bolts in the bed. This was not a proper repair, nor was it good for the engine mounts. Thirdly, it is very hard to re-tap the embedded steel plate if you are adding “new” holes, which we learned the hard way when we broke a tap into the steel plate while installing the Beta. What should have been a simple procedure, ended up taking a full extra day to cut out the broken tap and glass the hole. We then decided to completely abandon the idea of tapping into the steel plates and moved onto using lag bolts. Lag bolts indeed have their shortcomings, mainly from them coming loose due to vibration or breaking if you over torque them. They are simple to use and as long as you know of the shortcomings you can live with them. Every oil change (100hrs) I would check to see if they had becoming loose, and I never need to tighten them down more than 1/4 of a turn.
We had success with that engine bed arrangement for nearly 500hrs. However, around 200hrs (3 years into service of operation) we developed a transmission leak from the front input seal. Shortly after that we noticed the transmission oil became very dark and smelled burnt, our TMC60 was overheating. Without getting into too much detail (because the engine was now 3 years old and only had 200hrs) it was considered out of warranty due to time elapsed. This meant any repairs or replacements were on my dime and clock.
Because of this we took off the transmission to see what damage had been done. We took it up to the yard’s workshop and they graciously allowed us to painstakingly disassemble and inspect all the internals. Usually an overheating gearbox indicates one of two things, overpowering of the gearbox or slipping clutches. Once our transmission was apart, we found that the clutches looked good, which left us with overpowering as the issue. We replaced the seals, reassembled and added a transmission oil cooler, which uses raw water to cool the oil sump of the TMC60. After reassembly we motored up the ICW to Annapolis and put another 100hrs on the new setup, but before the first oil change I could see the gear box was still overheating. By the time we got back to NC we believed the fwd gear was slipping. During our trip south we were not able to get Prism up to the speeds we were used to and we could over rev the engine, meaning the torque was making it past the gearbox. By the time we pulled back into the boatyard we knew we needed a new gearbox.
Picking a New Gearbox
Picking a new gearbox is something that you hope you never have to do because it’s quite spendy. Not to mention if you want to change the model you have, you will undoubtedly need to change how the engine is mounted and possibly the length of the prop shaft. So, the things you are looking for when searching for a replacement can be found in the schematics, they are:
1) The length of the gearbox from input flange to output flange.
2) How much “drop” it has vertically from those two areas.
3) the physical size of the gearbox for clearance of the hull
If the length of the new gearbox is 30mm longer from input to output flange, the shaft will be pushed out 30 more millimeters than your current arrangement. If the flange has 15mm more drop, your engine will need to be raised another 15mm to have the same angle.
I did not want to go with another TMC60 as the first one didn’t last long. After further research I learned that even though Beta Marine paired the TMC60 transmission with my Beta35 engine, that gearbox coupled with my reduction ratio (2.5: 1), has a power rating way under 35hp in continuous use. As in, it is rated for only 17hp!
The term Continuous Use also known as Commercial Use is important for a cruiser, Why? Well, us cruisers want to, at times, actually use our engine for over 24hrs continuously, which is what the term Continuous Use specifies. Beta however, obviously uses the “Pleasure Use” (1-3hrs of use) category when pairing engines to gearboxes. Now to give them credit, they are probably right in most cases as most boaters probably don’t use their engine for more than a couple hours at a time. However, the difference between continuous and pleasure ratings are nearly a 40% less of the accepted HP of an engine. So if the pleasure rating is 38hp at 2.5: 1 ratio, the continuous rating is 22hp at the same ratio.
Prism spins a large prop (20’’) and after a long talk with twindisk, (the parent company of Technodrive) we learned that our gearbox was undersized for our intended use. When I started to look for new gearboxes the choices were vast, but without wanting to buy a new prop shaft the options became much narrower. I had the choice of going with a hydraulic gearbox from PRM (PRM150) which would require me to buy a longer shaft, add an oil cooler exchanger and rebuild the engine beds, as that gearbox had less drop than the TMC60. Or, I could stick with the Technodrive brand and move up to their biggest mechanical gearbox, the TMC260.
When Twindisc bought the Italian company Technodrive, they asked their new engineers to redesign the MG-360 which was the original American gearbox design and was turned into the TMC 60 and the larger TMC260. Beta pairs the TMC260 with their larger engines starting with the 70hps, but again looking at the chart supplied from Technodrive for continuous use, the most horsepower you should pair with a 2.5: 1 TMC260 is 34kw or 46hp. Which is perfect for our 35hp, but not great for a 70hp.
I found a new old stock TMC260 from a Beta dealer up in the North East and it was shockingly in the reduction ratio I wanted, a 2.5:1. For $1100 I had the new gearbox shipped to the boatyard. Another thing I would have to change in order to use the TMC260 was the drive plate. The TMC60 has a 10 spline input shaft, whereas the TMC260 has a more robust 20 spline input shaft. After a few measurements and a call to PYI, I had a custom drive plate on order from R&D in England (cost about $300). It should be noted that the TMC260 is about 1/2’’ longer than the TMC60 and has 1/4’’ more drop. The case measurements are about 25% larger than our fried gearbox, but I was fairly confident it would fit in our hull. The best part was that I did not need to buy a new shaft nor was an oil cooler needed.
New Engine Motor Mounts
We have never been happy with the mounts we received with the Beta, back in 2016 nor the ones we replaced them with back in 2019. The originals where undersized and the ones we replaced them with where extremely stiff.
Jon did a deep dive into researching anything and everything about engine motor mounts, only to find that in the US, most options come from Vetus. When he finally landed on the type he liked, he called to make sure there were at least 6 in stock ( 2 for spares). The distributor confirmed that they did have a total of 6 and could send them to us the next day.
When we received them in the mail we were a little more than confused, as they were all a bit different. Come to find out, the model we wanted and ordered had been re-designed, and we received 5 of the original and 1 new.
Lucky for us, these mounts were just a bit to large for our space anyways. We returned the 6 and ordered another 6 in the smaller size.
New Engine-Bed Design
Jon spent many hours thinking of ways to improve the engine bed situation aboard Prism. He is always thinking of ways to make standard maintenance and future upgrades easier to do. Here is how his mind put it all together:
At first I was just going to add another 1/4’’ to the front shims already in place, the rear mounts had enough adjustment room to make up for the 1/4’’ drop without adding shims, so the swap was going to be very straight forward. Now, because I had access to a cherry picker as well as a large work tent (we were in the process of rebuilding a second HC33), I opted to remove the engine entirely. At this point we have removed our engine multiple times and have a good system. We had the engine out of the boat and in the shop within an hour, somehow everything went to plan. As I finished up the gearbox swap, I turned my attention to the engine beds and began to think, which is always slightly dangerous. Luckily I had a friend in the yard to bounce ideas off of, Kevin.
Kevin is an engineer who worked for Lockheed Martin and now works for NASA and specializes in vibration control and works with resin and fiber. So, if I ever wanted to redesign the engine beds this was the time to do and Kevin was the guru. After lots of napkin designs we both agreed on one. Working within Kevin’s parameters for the system to work and be safe, I came up with how to install it, keeping in mind I had to work within the footprint of the available space.
On the HC33, the engine beds were glassed down before the bulkheads were installed, meaning the beds butt up against the cabinetry inside the engine compartment. Staying within the requirements of having at least 3’’ of tabbing space, it was clear I could not simply cut out the old and install the new, but in-fact utilize the old in order to build the new.
Now before we go on, it’s important for you to know I don’t write technical articles and this project, at least to me, was fairly complex. If I did not have as much experience with glassing from the three major refits Shannon and I have done in the last 12 years, as well as 100s of more hours working on other boats, I would not have undertaken this project.
This project was at the upper end of my expertise and without Kevin’s extremely helpful advice and his vastly superior experience, I know this project would not have been as successful as it ended up being. If you become confused with my writing I suggest studying the photos as I feel like I did a fairly decent job documenting my progress.
I wanted to change the engine beds for a number of reasons. First, I wasn’t a big fan of the lag bolts, sure they work, but are not ideal. Second, having each engine mount on individual platforms made alignment a real challenge, as well as not knowing if every mount was at equal height. I had suspicions that I was getting an uneven load on my engine mounts. Third, anytime water came out of the mixing elbow and landed on the rear engine bed it would go into the holes, so I suspected rot was happening as well. Lastly, some of the lags had begun to free spin, meaning I needed to address fixing those before I could put everything back together. All these things seem fairly trivial now that I write them but at the time it was driving me nuts.
I wanted the engine to be mounted on 90° angle plates, specifically stainless angle plates so rust wouldn’t be an issue and I wouldn’t have to paint it. If I could do this, I would have a very flat continuous surface for all four engine mounts to rest on. This would also allow me to easily modify the plates in the future for different engine mount configurations, and if we re-power again in the future. This would indeed be the most universal engine bed system I could come up with.
The engine mounts needed to have about 3’’ of surface to mount onto, so I decided to buy 4’’ wide by 1/4’’ thick stainless steel 90° angle plates. First I needed to embed a 3/8’’ stainless steel plate into the walls of the original engine beds. These plates will serve as the “anchors” for the 90° plates to attach to. These plates would be tapped with 24, 1/4-20 holes in a 1×1 zig zag pattern. These plates would be recessed into the wood core of the current engine beds, glued into place with thickened epoxy, fastened with wood screws and laminated over. In order to get equal spacing as well as proper alignment to the shaft and each other, I had to weld spacer bars that utilized two of the already drilled and tapped holes per side. These spacer bars would have to be exactly the same length and have welded tangs on the ends that needed to be exactly 90 degrees. Any deviation in these spacer bars would mean that the 90° angle plates that are to be bolted to the recessed plates, would be off from one another.
When I mocked up the spacer bars, I welded them myself using aluminum welding rod and a torch. This was a terrible idea but I no longer had my tig welder onboard. I would not suggest using the aluminum welding rod becuase as I was attempting to weld 1/4’’ aluminum plate to 1/8’’ aluminum 1×1 angle. The 1/8’ almost always melted before the 1/4’ got hot enough to stick. What was supposed to take minutes took a day fiddling with this. If I had any type of welder this would have taken me 5 minutes max with mild steel.
To figure out where to place the recessed plates into the existing beds, I had to get an idea of the shaft angle coming from the stern tube. This angle is extremely important because if I could match it in line with the beds, there would be less potential for shaft binding and would make alignment that much easier.
The most simple way to get this angle was to remove the cutlass bearing and packing glad to expose the stern tube, get a tapered wood plug from the emergency kit and drill a hole in the exact center of it. Then, screw a small threaded eye into drilled hole and tie a string to it. Then thread the string through the stern tube so that the plug is on the outside. Next, I used tape and put a cross hatch pattern across the inside stern tube making the center square about 1/2″ X 1/2″. When I pulled the string the wood plug centered itself on the stern tube, and all I needed to do was place the bitter end of the string so it was hovering in the center of my taped cross hatch. This string represented the shaft and all of my placement measurements would be based on it. This was the best method I had without a laser bore sighter.
This next part required a fair amount of math. I needed to take into account, the shaft height, all the figures of the gearbox flange drop, the engine bracket height in relation to flange, and the engine mount stud engagement height, to allow for the most amount of adjustment. The amount of stud height on the engine mounts is important because you want to make sure you are setting the 90° angle plates to allow for maximum adjustment as well as hopefully having the engine sitting where the mounts are most effective for vibration reduction. I switched to Vetus KH-75 mounts, veering away from the much smaller mounts the Beta came with. These bigger mounts are perfectly suited for my arrangement and are readily available and are not that expensive. Looking through the white paper for the mounts you will find the minimum and maximum height, average the two and you get the optimum height, so that is what I shot for.
Prepping the Engine Beds
Now that I had my measurements, shaft placement and a game plan, it was time to start cutting. I started off by grinding down the entire engine bed area back to bare glass because I planned on repainting. Removing old paint completely is the best way to guarantee best adhesion for new paint.
In order to make room I had to cut down the aft beds a fair amount. The metal plates that were on top of the beds had to be cut out as they were put in with lots of resin. Making a cut in the center then prying out the plates seemed to work best. Once the plates were out of the wood, the core was exposed. I outlined where I wanted the recessed plates to be on the inboard face of the beds. I used an angle grinder with a metal cutoff wheel and cut the outside glass laminate off.
Now the wood was exposed on the top and the sides of the engine beds. I used a 1/4’’ drill with some tape to set bore depth and proceeded to bore holes into the wood core to the depth I desired. After I had all the holes bored, I went in with a chisel and or an oscillating multi tool to remove the wood that was no longer necessary.
Never put power tools on a ledge
While Jon was working his little booty off, he started to get tired…and that’s when accidents happen.
Jon was almost done with the nasty part of this job when the 5″ bosch sander took a chunk out of his head. Jon placed the very heavy tool on the top step of our companion way, which he has done a thousand times. Yet this time, he must have forgotten he was working directly under that top step. He somehow pulled on the cord and brought the 4lb tool down the 3 feet and caught it with his skull of course with the only sharp metal piece on the tool.
The picture to the left is after I cleaned him up, using super glue and tired his hair together. Normally I am not one to get “sick” from blood or cuts, in fact, I tend to get a kick out of it ( I should have been a nurse or something) BUT this cut I will admit, flipped my stomach, it was quite deep, probable should have had stitches.
But the superglue and hair knots saved the day, and Jon was able to get back to work.
Making the Metal plates
This next part I did all in the shop, on a $100 drill press, a $20 vice, and a few C-clamps. I did buy a pack of 1/4’’ cobalt bits as well as 11/32″ bits as I was going to be drilling about 50 holes into stainless steel. Scratch that, 100 holes as I had to drill the plates as well as the 90° angle. Luckily, I only ended up using one bit from each 10 pack, not bad for amazon special cobalt bits.
I started with mocking out my hole pattern on the plates and drilled the 11/32″ holes. Then c-clamped the plates to the 90° angle plate, using the 11/32″ holes from the plate as a jig to transfer the hole pattern to the 90° angle piece. After that I bored the holes on the 90° angle plate out to 1/4’’ and then tapped all 24 holes on the flat plates, which went remarkably well as I bought a set of high quality stainless taps from mcmaster. I also punched two holes at the front and back of the flat plates and countersunk them for the wood screws which I would use to dry-fit and also hold everything in place while installing and glueing. I repeated this process for the other side.
Dry fitting and Laminating
Into the boat I went with my metal in hand. I dry fitted for hours making sure I got the angle correct then drilled the wood screws to lock in the flat plates. I inserted sharpened studs into the plate which I made out of cheap 3’’ 1/4-20 hex bolts by cutting the tops off of and sharpened on a grinder. These pointed studs did two things, they plugged the threaded holes so no resin would ingress into the threads, they also would help punch holes into the laminate when it came time to glass over the plate. With the studs inserted and threaded (to allow full thread engagement), I put heat shrink on the shafts of the studs to prevent the resin and glass sticking to the studs.
I unscrewed the studs for the last time, prepped the plates by sanding the surface with 80grit and wiped down with acetone, now only handling with clean gloves. Before installing I added a bit of quick drying silicone sealant to the threads and threaded them into the plates. This would guarantee no resin would get into the threads, thus making the studs impossible to remove. After 30 minutes the silicone dried and I was ready to install.
I mixed slow epoxy from US composites and first coated the wood in the areas behind the plate. Once coated I mixed in some cabosil thickener and coated the area again. Placing the plates lightly in and just barely threading the wood screws to hold them in place I got the spacer bars ready. These bars utilized 8 of the already threaded holes on the plates, and since these holes were not plugged like the rest I used a little tape behind each hole to prevent resin coming in. For added security, I also coated the threads of the bolts that I used with petroleum jelly as a precaution. With the spacer bars in place, I grabbed my trusty string and sighted the center of the spacer bars which were previously marked and represented the alignment of the prop shaft. Slowly I tightened, similar to using sights on a gun, everything was tightened while keeping the line straight with my two center marks on the spacer beams. I then cleaned up the resin behind the plates, making sure I had even squeeze-out everywhere, any area I wasn’t happy with, I packed in more resin.
Because it was so damn hot, the thickened epoxy started to gel about an hour later. With the wood screws firmly in place, I felt comfortable removing the spacer bars at this point. I put the remaining studs into the 8 holes that held the spacer bars with a little silicone on the threads. All that was left to do was to add the fiberglass and laminate it all together.
We needed 1/4’’ of layup to get the thickness and strength I wanted for this application. We decided to use 1708 in conjunction with 8oz biaxial. We did six layers of each, twelve layers total. The 8oz is kind of a tricky thing to work with as you need to add thickened epoxy with it to avoid air bubbles. This allows the thicker 1708 to bend more easily around corners because the thickened epoxy acts as a binder for the layers on either side of it. The 8oz acts as a stiffener and as a grid for the thickened epoxy so the 1708 doesn’t want to slide around. Shannon and I added the layers as a team, Shannon would wet out the glass and I would lay it up and punch through the sharpened studs on the lower part. We broke each side up into two parts, a fore and aft section so the pieces of fabric would be smaller to work with. By doing this we were able to alternate the overlap area by 3’’ in the center so there would be no bump and the two pieces would be structurally woven together.
It should be noted that I tapered the fiberglass around where I was working with a grinder beforehand so that there would not be a hard lip of where the new glass work began. Each layer was 1/2’’ smaller than the next with the smallest layer allowing a 3’’ tab over the original glass, at this final layer the thickness would be 1/4’’ throughout.
I’m not going to lie, this part was hard and only got harder as once we finished one side, the person who was placing the glass lost room to support themselves as a large section of the workspace was now off limits to touch. By the end of all 12 layers I was absolutely spent. Shannon finished with the fin roller to get the air bubbles out before we applied Tile clad HS epoxy paint directly to the surface of the curing resin. Doing this avoided the need to sand or use peel ply, and also has the added benefit of creating a chemical bond between the two chemicals.
With everything cured I removed the studs with pliers, this was the most stressful part as I had never used this method (this was from Kevin’s trick book) but to my relief they all came out without a hitch. We cut off the leftover heat shrink ends that came out of each hole with a multi tool and ran a sander over the surface to flatten it. I threaded a 1/4-20 flat tip tap though each hole just to clean them before moving on.
Now the engine beds were ready for a dry fit with the 90° angle plates confirming with all 48 bolts. My suspicion of the two plates not being exactly flat across the horizontal plane turned out to be correct and they needed to be trued (matched) to each other. I found this out by using a straight edge across the top of the angle.
To correct this I used thickened epoxy. I found the correct amount of adjustment by simply adding washers under the forward edge of the angle plates on the fiberglass beds. Once I found the right amount of shims to correct the angle, I taped the washers together and then taped them to the engine beds. Upon removing the angle plates from the beds, my shims were left in place for the next step.
Inserting the sharpened studs again into the embedded plate, I covered all 48 of them with petroleum jelly along with the back of the angle plates that mated up with the engine bed, then slathered thickened epoxy on the engine beds around the studs. Sliding the angle iron over the studs and into place I pressed lightly, then removed the furthest forward and furthest aft stud, replacing them with a jelly coated hex bolt, I slowly tightened down and watched good squeeze out around the entire plate. Once both sides were done, I checked to see if the plates were true to each other again with a straight edge. It showed that they were well within the margin I was shooting for. I just barely could see light at the outboard edge of the angle between the straight edge.
I waited until the resin was a bit gummy before I began to pull the studs. I was definitely a little more concerned about getting these studs out before the resin cured completely because if they got stuck I would be in real trouble. To my relief, all 48 came out just fine and when I couldn’t put a fingernail into the resin anymore I pulled off the 90° plates, leaving me with a perfectly flat and shaped surface.
Installing and Alignment
Now that the glassing was done all that was left for me to do was to drill the holes for the engine mounts into the 90° angle plates. Using the string from before, I made a grid on the top faces of the 90° angle plates in correlation to my shaft angle. This would provide help to make sure I got the fore and aft bolts perfectly aligned before drilling, and that they were in fact in line with the prop shaft, not with the 90° angle plates.
With the grids made, I set the engine mounts to the heights I believed they should be according to my measurements and then lowered the engine back in place. This all went without a hitch and now that I had a continuous piece between the front and back of the engine beds, all I had to do was to get the rear engine mounts on the front of the new 90° angle plates and slide the engine in. Whereas before I had to keep the engine entirely elevated until it was over the aft beds which was hard with the beta, nearly impossible with the old Yanmar. With the engine in place I did a quick alignment with the engine floating (held by gravity, not bolted down) on the new plates.
Once I got it to the place I used mimic punches to mark where I wanted the holes. Before punching I made sure that each hole was on the same line of the grid fore and aft as well as both front mounts matched the same athwartship lines on the grid. Again this made sure the mounts were aligned with the prop shaft. With the plates dimpled by the punches I removed the engine once again and brought the 90° angle plates back to the drill press in the shop. I drilled the holes and tapped them with 3/8-32 threads. I used fine threads as I had only 1/4’’ of metal I was taping into so I wanted optimal thread engagement. I also used Bumex 88 bolts as they are much stronger than standard stainless and I was confident in their thread retention. With the holes tapped, back into the boat the 90° angle plates went. Using fender and lock washers as well as some blue lock tight, I bolted the 48 hex bolts through the plates for the last time. Once the engine was back in place we were ready for the final alignment.
Due to weight, the motor mounts exhibited a bit of sag. I had to go up the studs about a 1/4’’ from the original settings I did when the engine was free floating. This was more than I expected but still well within the specs of tolerance the engine mounts allow. The engine being on the 90° angle plates also made precise adjustments so much easier than before, a small nudge and things just moved, all 4 mounts at a time, lovely. After getting the best alignment I have ever achieved, I bolted down the mounts and the engine bed upgrade was done.