Inboard Prop Shaft Thrust Bearing/Mount & Hydraulic Get Home

Hello,

This is my first post, I'll try to be a brief as possible.

I'm rebuilding a 38' diesel/fiberglass trawler in hopes of actually moving aboard it full time someday soon. It's a full displacement, single engine design. The engine was originally mounted on solid steel mounts bolted solidly to the main stringers. I'm going to install a DriveSaver or similar vibration reducing coupler and rubber mounted vibration reducing engine mounts, all of which means I'll be moving the engine forward a few inches. I'm interested in also building and installing a strong solid cross-member to take the thrust/pull of the propeller shaft rather than having it being transmitted to the transmission. While doing this I want to add a large sprocket to which I could add a chain-driven hydraulic drive at a later date.

So, I have couple main questions that I'd like to pose to the forum;

1. Does anyone know a good source for the large thrust bearing (which would handle not only thrust but also pull if the shaft / boat was reversed? Any brand names, sources or better yet actual links to their websites would be appreciated. Does anyone have any photos of such a setup that they could share?

2. As for the hydraulic drive. This is only a 38' boat and I don't have (at least at this time) a large generator on which to drive a single large hydraulic pump. I do however have a few small generators, a 7.7kw Westerbeke and two 3kw Onans (one of which is being converted to a dedicated DC 250 amp generator). So, is it possible to put hydraulic pumps on all three of the generators in hopes of getting enough power to at least run the boat 2 to 3 knots? My hull speed is about 7.6 knots. Ideas? Comments?

Thanks
DieselTrawlerGuy

 

I sounds like you will be moving the engine more than a few inches. You will need clearance under the shaft to hang the auxiliary drive sprocket, then you will need to add a short universal shaft to connect the soft mounted diesel to the fixed prop shaft. The tube needs to be long enough that you can telescope it enough to slide it on and off the splined shafts. So I'm thinking you need about 3 added feet. You didn't mention any HP figures of shaft and prop sizes, but you can putt-putt along on 5 hp auxiliary quite nicely if you want to design around doing that. It will impact how you set up the driveline though. You can't expect the governor response of the prime mover and the governor response of the auxiliary to both just match up to each other and the boat's load variations, you need some design savvy to develop a driveline that is amenable to both systems. With the quality of modern small diesels, though, I question the need to soft-mount the small prime mover in a trawler. The system you are describing is more often found on high-powered sport fishers and fast yachts. They also have decent off-the-shelf PTI systems for engines starting around 500hp. Rooting around a bit, I found one system for smaller engines that I haven't seen before - Transfluid HM560 and HVM700

http://www.transfluid.us/wp-content/uploads/2015/06/brochure-ibridoelettrico_USA_LQ.pdf

 

Hello PhilSweet,
I have no idea why you think that I have to move the engine/trans 3', I figure I only have to move it forward about 6" if I use only the thrust bearing / cross-member setup, possibly up to 12" if I use a short CV shaft in conjunction with the thrust bearing. As for horsepower, it's a 210hp Caterpillar 3160 NA with a TwinDisc 506 gear with a 2 to 1 ratio. And not that it has much to do with it but I have a 2" stainless shaft turning a 24" x 19" x 4 blade propeller.

And no, I don't expect an auxiliary hydraulic drive to turn up the same RPM and HP as the main engine, it's a Get-Home, not a spare engine/twin. For the Get-Home I intend on adding a large sprocket off of a Harley-Davidson motorcycle, they'll easily handle 100hp, far more than I'll have available from an auxiliary hydraulic drive. And it will be a chain sprocket, not a toothed belt like the newer Harley's all have. The chain can be removed without disconnecting the propeller shaft. Plus, I can use the sprocket as a shaft brake by adding an extra tab with a bolt hole that lines up with a hole in the sprocket.

The reason for installing the rubber vibration mounts is to cut down on both noise and vibration. The reason for adding the DriveSaver or similar vibration reducing coupler is the same, noise and vibration but with the added benefit of saving my transmission and engine in the event of a large propeller strike such hitting a submerged log or whatever.

And as far as the Transfluid HM560 and HVM700, if I wanted all of that complexity I could simply add one of the divorced transfer cases from a large 4x4, but I don't need that.

So, back to my original questions;

1. Does anyone know a good source for the large thrust bearing (which would handle not only thrust but also pull if the shaft / boat was reversed? Any brand names, sources or better yet actual links to their websites would be appreciated. Does anyone have any photos of such a setup that they could share? I really don't want to pay thousands of dollars for the AquaDrive, but I want something just like it. I have added photos of the AquaDrive as well as the new engine mounts I'm installing.

2. As for the hydraulic drive. This is only a 38' boat and I don't have (at least at this time) a large generator on which to drive a single large hydraulic pump. I do however have a few small generators, a 7.7kw Westerbeke and two 3kw Onans (one of which is being converted to a dedicated DC 250 amp generator). So, is it possible to put hydraulic pumps on all three of the generators in hopes of getting enough power to at least run the boat 2 to 3 knots? My hull speed is about 7.6 knots. Ideas? Comments?

Thanks
DieselTrawlerGuy

 

I was thinking you had maybe 40hp based on the description, which is where my space concerns came from (and my wondering why you'd bother). The Aquadrive unit for your Cat will be about 2 feet long based on their specs page. If you wanted to save money, it will be longer - you are paying for that compactness. But you get one stop shopping for matched motor mounts.

I know the limp home system isn't as powerful, but it still has to be matched for torque, rpms, and inertial loads. And the torque perturbations from a seaway are proportionally much larger at very low speeds , so torque response becomes a concern. Basically, you need the same range of torque variation at the shaft in both systems, which may entirely determine the gear ratio of the hydraulic system, not the power. You may end up with a design point that is only a fraction of the power of the system in order to handle the surge in torque. This isn't a hugely difficult thing to get to work, But I suspect you need to look at 25+ hp systems and not the 5 hp I mentioned earlier. I don't think you will find any info on setting up systems with more than a 10:1 power ratio. This is why you need to know the prop and shaft specs to figure out the setup.

 

Just to throw another idea into the mix (although I appreciate that buying a second motor/shaft assy may not be your need), I thought I'd outline what I'm doing to obtain the same level of redundancy that you're after.

I'm building a 38' Hartley and have a new Cummins 6BT39M (330HP) with a 10 degree downbox on the back of it. The gearbox also has a large hydraulic pump on the SAE drive. The gearbox output flange will drive a shortened truck UJ-sliding shaft-UJ assembly which I made from shortening a truck shaft (the truck had been in the 800HP range). On the rear of that assembly, the UJ flange mates to a 80mmOD/50mmID shouldered adaptor which is held by a 22216 E SKF Spherical Roller Bearings Cylindrical Bore - Bearing King https://www.bearing-king.co.uk/bearing/22216-e-skf/2086 bearing which in turn is held onto the hull/engine-mount frame with some serious steelwork.

Then I have a second motor - a M2.06 Vetus/Mitsi which is good for about 24HP @ 1800rpm. That has an identical hydraulic pump on the rear. So two hydraulic sources. These both feed into a large valve block which has various outputs - genset (flow controlled electronically to get stable rpm), anchor winch, bow thruster and finally, a secondary hydraulic motor driving a 25mm prop shaft and 12" prop. This secondary setup will sit out on one side of the main prop and I accept will produce some drag although a folding propr would sort that out.

So in terms of redundancy, there are two power sources, two drive-trains.

To answer your question DieselTrawlerGuy, go take a look at that SKF unit which the bearing experts have told me is seriously over-engineered for my 330HP setup.