Sliding Outboard Bracket

As opposed to swing sled brackets I'm thinking of making a slide down style bracket with the bottom of the bracket ending with the motor powerhead behind a small fixed nacelle.

There are lots of ideas on how best to make the sliding mechanisms from simple to ball bearing travelers cars. Since I am planning to use 2 motors the idea of 8 or so traveler cars to buy, etc is not a pleasant thought.

Anyhow, if anyone has any ideas or better yet pictures. Please post them.

Cheers,
Jeff

 

This was a common trend in the 70's and 80's with reversed transom sailboats. The engine was mounted to a sled, which had female tracks installed on the backside. These fit over their male counterparts screwed to the transom. The tracks looks much like jib sheets tracks. I don't remember any with cars and tackle, though I imagine the heavier engines needed some help.

 

My Macgregor 36 cat had a sliding bracket on the stbd transom, it was a simple affair that worked quite well and was made out of 1" ss tube like a bow rail, ive seen them with one on each transom.

Steve.

 

Why not swing? Easier and no hardware to buy

Then again my mate made his own tracks - SS 1 inch tube with composite tube sliding over it. The tube was glassed to a composite outboard mount. If you are clever you will only use the tube to raise the motor. To handle the motoring loads you would get the composite mount to wedge into the nacelle - a sort of trapezium shape would do. I love the wedge on my rudder cassettes - no slop and no noise. Raise it 5mm and it goes free easily. Go the wedge!

cheers

Phil

 

I've seen a few that used genoa track with adapted genoa cars for sliders-the non rollerbearing kind one at each corner of the OB mounting nacel Nylon slides on some. The weight of the motor sends it down and the fit lets the tackle hall it up. Bigger boat gear like 1 1/4" track can take a big load which you need to take the pitching of heavy seas. It is a older set up. The parts can be sourced used, stainless track won't have the finish wear issues of aluminum. Lots of ways to do it. Phil gives out wedgies.

 

I owned a McGregor 36 with the sliding arrangement described by Steve W and it was a simple device that worked well, but it did have its flaws.

I have also operated boats with sleds and they are infinitely easier to use and absolutely simple and trouble free.

The more moving parts, especially in an area so prone to corrosion, the more maintenance and potential for problems. The McGregor bracket would jam sometimes and the location made it very difficult and sometimes dangerous to kick it free, and that with a 9.9 on it.

If you have a nacelle anyway, incorporate it into a sled, you'll be happy you did.

Steve

 

the sled is still an option, but I'm not real keen on two engines on one sled?

the other reason for the slid, is the powerhead will be that much further above the WL offshore and all water will drain from the powerhead when shut down.

I was thinking of something where the bracket would wedge into the nacelle. It seems to me if you make something with tube or pipe, the time and cost would be the same or less than a swinging bracket. also the motors never need to tilt either.

cheers,
Jeff

 

The basic Mac 36 bracket did have a few issues but mainly because of a lack of precision but i made a few mods that made it work flawlessly, as i recall it didnt get the prop clear and i still needed to tilt it because of the macs low freeboard.

Steve.

 

I was going to have "wells" of sorts in the front corners of the cockpit. Actually square lockers about 36" high so maybe 20" higher than the cockpit seats. Richard has many of these on his designs so you can better work the winches, but not quite this high.

It's all just conceptual at this point, but if the bottom of the nacelle was say 10" above the load WL, the prop would be covered by the nacelle and the top of the motor cowling would be just under the hatch. The cockpit is fairly short at around so with swinging brackets, the motor would be hanging out past the aft beam when up and make landing dinghys, etc more difficult.

 

If your nacel has sides here is a idea, simple inexpensive bracket/tracks. The powerhead is clamped on to an inner box that should have provisions for air flow. The "tracks" are simple stainless channel stock inset into the sides of the nacel and well, they don't need to be very deep. The inner box has plastic/nylon strips with countersunk bolts fastening it to the sides, it should be inset to spread the sheer loads off the fasteners. This is your inner track and bearing rolled into one. Wider is stronger, it doesn't need to be very deep, long is good to spread the torsion loads . Black plastic is better for UVs.

 

So who is designing your boat - you or Richard Woods?

Presumably you mean 10" above the WL with the motor bracket raised since you wouldnt want the prop covered by the nacelle when it is lowered. Isn't 10" a bit close to the water to avoid waves splashing against the nacelle and causing extra drag when sailing? Most people seem to think that the space under the bridgedeck should be kept as clear as possible. Having the raised props hanging out behind the aft beam might be a bit of a nuisance with the dinghy but at least it would allow for easy clearing of ropes/debris from the props.

Another question, only indirectly related to the motor bracket design. One of the reasons for having two engines on a catarmaran is to enable tight turns at low speed by use of the engine controls. I have seen it reported (Can't remember where though) that even with inboard engines on the hull centrelines it can be hard to turn a catamaran through a strong headwind with the engines alone. Bringing the engines into the cockpit, the spacing between the props is reduced. I wonder how far you can go in that direction and still have the advantage of good low speed manouverability in windy conditions. Practical experience would be of interest.

 

I'd go with John on the question of your nacelle. On Kankama it goes right down to the water when motoring and then 300mm up and out of the water when sailing.

When I first put the new nacelle on I simply bolted it to the underwing and it was 70mm above the water. It was terrible. At anchor it would slap on chop - offshore it would bang. Now the pivoting nacelle hardly even gets wet and the powerhead of the engine is mostly above the bridgdeck bottom.

I had the same problem with the powerhead protruding out behind the aft beam - I made an aft deck there out of Duflex - great spot for the dinghy - just keep it light.

Personally I can't really abide all of the space that twins take up inside a cat. Kankama has one motor mounted under the cockpit seat. Sisterships with motors on tracks have quite a lot of interior space used up with the well. Here is a link to a boat by the same designer with motors like you describe. http://www.brucearms.com/content/photo-gallery

cheers

Phil

 

On the twin engine single sled arrangements I have seen, mostly older Gold Coats Day Charter Cats, the engines steer, which is very effective re maneuverability.

As far a twin engines spread far apart, I had twin 9.9 Yamaha hi thrust on my McGregor cat on the hull transoms, Outboards just don't have any guts in reverse so the maneuverability you might think you would get just isn't there.

Steve

 

Richard is not real into mechanical details and seems to leave most of that to individual builders.
His stock outboard nacelle is quite close to the WL to try and keep the powerhead somewhat dry.