Yanmar V-twin diesel conversion of OMC Saildrive

[Dockhead]

Originally Posted by sgancarz

I know I saw the torque rating on the OMC somewhere, however I can't find it now. But using the formula TORQUE = (HP x 5252) ÷ RPM. ((15 x 5252) ÷ 3750 = 21), the OMC calculates to 21ft/lbs of torque.

Here is a good article that explains this formula and how it is used to calculate HP, as Horsepower is dependent on time. However when trying to calculate TORQUE it does not work quite as well, as torque is independent of time.

Horsepower vs Torque

Great discussion by the way. Made me do some more research and taught me a few things.

You don't need to go through those conversions, and I don't think you have any problem.

Gearboxes care only about torque, and are always rated for a certain amount of torque. I don't think they care about what RPM that torque is delivered at (within their operating ranges of course).

FURTHERMORE, you are looking at MAX horsepower and torque curves, which is not what these engines will do in real use. You should be looking at the propeller curve, which shows how much power is absorbed by the prop at different RPMs.

You simply don't have a problem, if you don't change the propeller. Changing engines does not change the amount of torque absorbed by the prop at any given RPM.

If you do change the propeller, then you just need to mind the maximum torque rating of the gearbox.

[sgancarz]

Last night I test fit the coupling and performed a dry run of the complete shaft alignment proceedure. I then disassembled the coupling to see how easy it would be to change a belt. Sitting on the stand in th garage was not too bad, however I am sure that doing it while laying on my stomach in the lazarette will be a completely different story.

Here is a picture of the Paraflex coupling installed. I still need to complete the pulley to drive the water pump">raw water pump.



Now I am finishing up the painting of the lower unit and will next be permanently installing the Iso-ring on the lower unit with 3M 5200 sealant. At that point the lower unit will be ready for installation. I then need to do a final sanding and paint job on the mount assembly.

Still waiting for warmer weather so that I can finish cleaning and painting the lazarette. Also need to install the thru-hull for the raw water intake and the new fresh water tank.

[Jesse]

I just noticed the lower unit is in a flexible mount. I hadn't realized that before. So as power is increased to the propellor the shaft angle will change, which in turn will change the location of the upper end of the shaft proportionally to the amount of power applied. The amount of movement could be small or great depending on the density of the mount. So basically there is a spun shaft on a flexible mount that will change it's angle and center, being driven by a flexibly mounted engine with admitted vibration issues, joined by a very nice coupling that dampens the vibes and accepts misalignment. There will be no middle ground on the results at all, It will be smooth as butter or go to hell in seconds. I'm rooting for smooth but advance the throttle slowly on the first tryout.

[deblen]

Originally Posted by Jesse

I just noticed the lower unit is in a flexible mount. I hadn't realized that before. So as power is increased to the propellor the shaft angle will change, which in turn will change the location of the upper end of the shaft proportionally to the amount of power applied. The amount of movement could be small or great depending on the density of the mount. So basically there is a spun shaft on a flexible mount that will change it's angle and center, being driven by a flexibly mounted engine with admitted vibration issues, joined by a very nice coupling that dampens the vibes and accepts misalignment. There will be no middle ground on the results at all, It will be smooth as butter or go to hell in seconds. I'm rooting for smooth but advance the throttle slowly on the first tryout.

Aha-Ask yourself how a saildrive transmits it's fwd(rev) thrust to the vessel.
or a shaft drive,for that matter. In small hp boats-via the engine mounts.
In hi hp vessels-via a thrust bearing securely fastened to hull & shaft.

/ Len

[sgancarz]

Originally Posted by Jesse

I just noticed the lower unit is in a flexible mount. I hadn't realized that before. So as power is increased to the propellor the shaft angle will change, which in turn will change the location of the upper end of the shaft proportionally to the amount of power applied. The amount of movement could be small or great depending on the density of the mount. So basically there is a spun shaft on a flexible mount that will change it's angle and center, being driven by a flexibly mounted engine with admitted vibration issues, joined by a very nice coupling that dampens the vibes and accepts misalignment. There will be no middle ground on the results at all, It will be smooth as butter or go to hell in seconds. I'm rooting for smooth but advance the throttle slowly on the first tryout.

This has been a concern of mine since the beginning. I originally wanted to mount the engine directly to the top of the drive leg, but not sure the Iso-Ring could handle the weight and additional torque of the diesel. So I opted for the current configuration.

With the addition of the Para-flex coupling, I think I am going to be ok. The Para-flex can handle up to 4 degrees and 1/8" of misalignment. The Iso-Ring seems to be pretty rigid, so not sure there will be much movement there, but once I get it mounted in the boat I plan on taking some measurements of the actual movement.

The plan is to mount a dial indicator on the mounting base and push and pull on the lower unit to see how much movement I actually get at the end of the input shaft.

[Jesse]

The plan with the dial indicator should tell a lot. Can the ISO-RING be compressed at all? That might offer some adjustment in its rigidity.

[sgancarz]

Originally Posted by Jesse

The plan with the dial indicator should tell a lot. Can the ISO-RING be compressed at all? That might offer some adjustment in its rigidity.

The Iso-Ring does compress between two halves of the lower unit and is also secured in place/sealed with 3M 5200. But as far as compressing it more that is not possible. It appears quite rigid the way it is, but then again I don't have a lot of leverage with it not being installed.

Maybe someone with previous OMC Saildrive experience could chime in on how much movement they have experienced?

[malbert73]

How did this work?


Sent from my iPhone using Cruisers Sailing Forum

[sgancarz]

Actually still a work in progress. I am however, getting close. I hope to have the lower unit in by next week. Lots of moving pieces with this project. Lots of parts to source with lots of trial and error. Lately my nemesis has been the drive pulley for the raw water pump. On my third attempt and looks like I am going to have to do some machining to get this one to finally work.

The weather has not cooperated much this year either. Temps have been up an down here. Also had to take a week off for a much needed vacation.

Hopefully will get a chance to get some work done on it this weekend. I will try and post an update early next week.

[sgancarz]

Well the lower unit is finally in. I splash the boat first thing tomorrow morning. Still quite a punch list left before I can install the engine. But, hopefully there are no leaks tomorrow. Here are some pics of the lower unit installed and ready for the water.

Also I obtained a NOS OMC folding prop earlier this month on ebay. This is a great addition to the project.

[deblen]

Originally Posted by sgancarz

Well the lower unit is finally in. I splash the boat first thing tomorrow morning. Still quite a punch list left before I can install the engine. But, hopefully there are no leaks tomorrow. Here are some pics of the lower unit installed and ready for the water.

Also I obtained a NOS OMC folding prop earlier this month on ebay. This is a great addition to the project.

Nice workmanship!

It appears that the Iso-ring hull seal carries the full weight & torque of the engine.
In a normal horizontal engine/saildrive setup,the engine would be on 4 engine to hull mounts.
Perhaps you will need 4 more mounts between your adapter & the hull?

Cheers/ Len

[sgancarz]

Actually the Iso Ring will only be carrying the weight of the lower unit. The adapter sits on top of the original mounting plate which mounts to the fiberglass foundation that is molded into the Hull. The engine will then be supported on the four mounts atop the adapter.

The engine only weighs 120 pounds, so really don't need the heavy stringers normally associated with a big cast iron diesel.

[deblen]

Originally Posted by sgancarz

Actually the Iso Ring will only be carrying the weight of the lower unit. The adapter sits on top of the original mounting plate which mounts to the fiberglass foundation that is molded into the Hull. The engine will then be supported on the four mounts atop the adapter.

The engine only weighs 120 pounds, so really don't need the heavy stringers normally associated with a big cast iron diesel.

Gotcha! / Len

[darylat8750]

Is one end of the U shaped mount made out of flat plate going to be boxed? We had a mount for made like that for a garage door operator and had much trouble until the designers stiffened the structure . I really think you need something in addition to the vertical plates for stiffness .

[Terra Nova]

It must be boxed.