Outboard well plugs. Examples, ideas and thoughts?

[Franziska]

Hi,

we have an upcoming refit this summer and consider moving our outboards into dedicated wells.
The boat is 35ft catamaran with deep vee plywood hulls.

At the moment they are quite exposed when operating despite sitting on a sled which moves up and forward behind a wave deflector.
Due to geometry this always kincks the cables despite some clever cable routing.
Lifting is currently helped by a tackle but really hard work.
No, there is no space for a hydraulic or electric actuator. We already looked into this.
In the new location that will be possible.

In the wells they will just slide straight up and down, and they will better protected when operating and the lifting will be easier.

Right now I am researching clever solutions for plugging the hole in the bottom of the very deep well when the 9.9 Yamahas are not in use.
Ideally that opens/closes almost automatic when moving the engine up or down.
Alternatively via a rope that gets pulled.

The solution does not need to be 100% watertight, but has to stop turbulence when the motors are up.
Neither should it rip off when open.

If you have (or know of) a boat with an outboard in a deep well, please share the solution you have, or have seen.
Please keep this specific to the mechanism plugging the hole.

I'm researching this, as to see some more solutions before coming up with our specific solution.

You can see some images of the current solution on our website www.ladyrover.com

Thanks.

[Adelie]

Is the bottom of the hull at the location of the wells vee’d too or is is flat?

[Dave_S]

My boat has the outboards coming up and down through the hulls. The origional design is to have an aluminium plate that matches the shape of the hull and overlaps the opening bolted to the outboard skeg so that there is a small amount of pivot and that the point of balance is forward of centre. This way when moving forwards the plate finds its least drag position but in reverse it moves to the worst position limited by the design restricting it's travel. Another issue is when lifted the outboard leg is still in the water always. You could over come this with a spring that allowed the outboard to lift higher against the spring but this brings all sorts of alignment and stability issues.

I discarded the cover plate and lift the outboards clear of the water. My intention is to fabricate reversed bombay doors so they lift up. I have agonised over the mechanism for opening and closing them for some time. I expect to build each door with 2 overcentre spring loaded snap open, snap shut mechanisms. The beauty of these is the mechanism does not need to be in the water or in the cramped well, it can activate with rods. I then plan to fit a self bailer to each side.

Not as simple as you might hope for. I would love to hear a better way, because this is a bit clumsy.

[Chotu]

With all my ruminating on clever design, this one has eluded me.

I currently have no plug in my outboard wells and find it doesn’t really affect the boat in terms of efficiency.

At 8 knots (motoring speed) I have done a lot of careful observation of the wells. Yes, there is some turbulence, but it’s minimal.

That said, I would still love to solve this problem in a good way. I had originally envisioned some kind of rubber skirt around the outboard for the down position. Definitely check your waterline in the well first to be sure of cooling the outboard properly.

In the up position, it’s got to be a plug of some sort.

I’m not a fan of anything protruding below the opening in the up or down position.

My compromise was to just cut the hole as small as possible given the geometry of the outboard leg. That ends up being a sort of T shape, but more like a lower case t, with rounded ends and no hook in the tail as the font here has.

Eagerly following this thread.

[Chotu]

I looked at your site

I have a word of advice about the proposed outboard slide. Don’t make the same mistake I’m fixing.

It’s quite important to find a way to add vibration damping to your outboard slide mechanism. Otherwise, the vibration of the outboard can be transmitted to the nearest bulkhead which acts as an acoustic amplifier and is extremely loud.

[Franziska]

Yes it is.

One of the thoughts II had so far is a folding flap.

The flap would need to be somehow retractable to the inside with a way to lock it in both positions.
Still it needs to be uncomplicated too. If it's not it will eventually fail.

.

Originally Posted by Adelie

Is the bottom of the hull at the location of the wells vee’d too or is is flat?

[Franziska]

Thanks. I'll keep avoiding resonance sounds in the back of my mind.

Regarding turbulence, I am not really concerned about the open position when motoring.
I am much more after avoiding an open bottom when sailing and the motor isinside.

The flap would than also help to reduce wave action going into the well and keep the area a bit dryer besides removing drag.

A thing I like to avoid is a cover which is fixed to the lowest point in leg and fully exposed to the stream of water when motoring.
It would probably not last long.

The other is a semi permanent cover with the outboard leg always sticking out like a sail drive. I could live with this only if there would be folding props for the Yamaha 9.9.
To my knowledge there are none on the market because it's a fairly unique problem.

Originally Posted by Chotu

With all my ruminating on clever design, this one has eluded me.

I currently have no plug in my outboard wells and find it doesn’t really affect the boat in terms of efficiency.

At 8 knots (motoring speed) I have done a lot of careful observation of the wells. Yes, there is some turbulence, but it’s minimal.

That said, I would still love to solve this problem in a good way. I had originally envisioned some kind of rubber skirt around the outboard for the down position. Definitely check your waterline in the well first to be sure of cooling the outboard properly.

In the up position, it’s got to be a plug of some sort.

I’m not a fan of anything protruding below the opening in the up or down position.

My compromise was to just cut the hole as small as possible given the geometry of the outboard leg. That ends up being a sort of T shape, but more like a lower case t, with rounded ends and no hook in the tail as the font here has.

Eagerly following this thread.

[Chotu]

Originally Posted by Franziska

Thanks. I'll keep avoiding resonance sounds in the back of my mind.

Regarding turbulence, I am not really concerned about the open position when motoring.
I am much more after avoiding an open bottom when sailing and the motor isinside.

The flap would than also help to reduce wave action going into the well and keep the area a bit dryer besides removing drag.

A thing I like to avoid is a cover which is fixed to the lowest point in leg and fully exposed to the stream of water when motoring.
It would probably not last long.

The other is a semi permanent cover with the outboard leg always sticking out like a sail drive. I could live with this only if there would be folding props for the Yamaha 9.9.
To my knowledge there are none on the market because it's a fairly unique problem.

My instinct is that leaving the leg in the water will result in more drag than an open outboard well with the leg clear of the water. It makes quite a difference in drag on my boat if the leg is in the water or out of the water.

I would search only solutions that keep the leg clear of the water. Your outboard will last longer too.


Maybe some rubber flap attached to the hull is the best solution?

Pull a rope to open the flap and deploy the outboard. When you raise the outboard clear of the water, you release the flap and it goes back into place?

The same could be accomplished with a spring loaded door also.

Keeping the well drier is a good idea. I agree. Mine is full of marine growth because I did not use bottom paint inside. I should have.

These threads are great because it gets you thinking about more ways to do things.

[Franziska]

Yep rubber flap is an idea, but it's needs to be fairly stiff, otherwise it will make matters worse.
An alternative would perhaps be 2 strips of delrin which overlap quite a bit.
Maybe with some sort of deflector at the front edge.

I thought about hinges as well, but they are likely to fail due to growth when constantly submerged.

I just thought about another idea. How about a fairly thin but stiff plate which slides forward along the keel and is guided by two U channels of sorts? A bit like a Guillotine.
Our hulls are fairly straight where it would be mounted.

Originally Posted by Chotu

My instinct is that leaving the leg in the water will result in more drag than an open outboard well with the leg clear of the water. It makes quite a difference in drag on my boat if the leg is in the water or out of the water.

I would search only solutions that keep the leg clear of the water. Your outboard will last longer too.


Maybe some rubber flap attached to the hull is the best solution?

Pull a rope to open the flap and deploy the outboard. When you raise the outboard clear of the water, you release the flap and it goes back into place?

The same could be accomplished with a spring loaded door also.

Keeping the well drier is a good idea. I agree. Mine is full of marine growth because I did not use bottom paint inside. I should have.

These threads are great because it gets you thinking about more ways to do things.

[Dave_S]

Originally Posted by Franziska

Yes it is.

One of the thoughts II had so far is a folding flap.

The flap would need to be somehow retractable to the inside with a way to lock it in both positions.
Still it needs to be uncomplicated too. If it's not it will eventually fail.

.

I believe the reversed bombay doors opening up is the best solution, hinges made from acetyl or similar will last quite well I believe.

And over centre spring latches will snap the doors open and snap them shut.

[Franziska]

Hey, thanks for that. Do you have a photo example of these spring loaded latches you mean?

Originally Posted by Dave_S

I believe the reversed bombay doors opening up is the best solution, hinges made from acetyl or similar will last quite well I believe.

And over centre spring latches will snap the doors open and snap them shut.

[Chotu]

Originally Posted by Franziska

Hey, thanks for that. Do you have a photo example of these spring loaded latches you mean?

Yes, I’m also curious about the latches.

Not sure why a double door is more ideal than a single door, however.

Why the bomb bay style?

[Franziska]

I'm not great in manual sketching, one of the reasons why I ended up working in CGI.

:-)

Here three crude sketches. Guess each of them could be built somehow in a way, that the hatch control lines are connected to the outboard bracket, so that they open or close automatically when the engine slides up or down.

Two sliding covers as section.

One as a fold down plug as longitudinal section.
Especially this one needs a locking mechanism, maybe a spectra line with a cleat would suffice.

Preferences? Thoughts?

[Montanan]

The turbulence of a well is modest. All swing keel and dagger board have an opening and they simply do not impact performance very much and those openings would typically be much larger than what the lower end of an outboard motor.

I perceive you are attempting a complex scheme which will avail little benefit.

It you attempt to seal of the opening, it will need to be capable of handling the entire dynamic displacement loading of the change in depth of the water with the passing of waves.

There will be turbulence caused by a protuberance of a sliding closure device. Of course what one would hope to achieve is a smooth surface aligned with the hull.

Bow thrusters often incorporate shaping of the hulls to mitigate against the eddy caused by the tunnel. One could look at their designs of the fairings on the hulls that reduce the drag formation of the horizontal tunnels for guidance and install such.

[Paul Howard]

Have you seen the outboard engine installation in the Tomcat 970 catamaran built in Newmarket, Ontario, Canada?
it is a sort of outboard engine in a well in the overhang, taking up about half the hull transom width beside the steps. The outboard is protected, there is extra buoyancy outboard and aft of the engines. Some adaptation of this might work for you.