Outboard well turbulence

[Peter Cockerton]

Whilst out on Rutland yesterday on a steady run i took some readings from my paddle driven log to see the difference the outboard, rudder, and centreboard made to my speed through the water. With outboard, centreboard, and rudder down i was making a steady 4.3 knts i lifted the outboard and speed increased to 4.8 knts. Outboard down again and centreboard up 4.6 knts, about the same with centreboard down and rudder lifted to horizontal.

With the outboard raised i still get a fair amount of turbulence in the outboard well, the lamelia if thats how you spell it is still in reasonable shape so i want to look at a way of reducing further the turbulence to reduce drag.

Anyone else considered this and have any ideas on creating a simple but effective method way of shuttering the outboard slot.

[Julian Swindell]

I made and fitted a plywood filler for my outboard well last winter as the flaps had largely broken up over the last few years. It is just plywood (painted White here) fitted into the hole and held down by a pivoting cross bar. Three isn't much room under the raised outboard to either place it our remove it, but it works quite well. I got quite adept at using it after a while and I use it most of the time, but if I am just out for a drift around the harbour I often don't bother. It its mainly useful when going fairly fast. I made it because I didn't fancy replacing the flaps. That seemed to involve a lot of funny glue.

[Peter Cockerton]

Julian

Thanks for sharing that idea with me, fairly straight forward and it works, with the turbulence affect removed if not the flow disruption under the boat do you notice any positive affects on the boat speed or any other aspect of the boat behaviour.

I note you comment on the amount of space and the filler being a little akward to get into place can you see it being possible to install a couple of channels front and back of the opening which rise partially curved vertically to hold a flexible piece of shutter material which could slide over the gap and when you want to use the outbaord be pulled up away from the opening, just a thought.

Thanks again

Peter

[Julian Swindell]

Hi Peter
I originally planned to have the filler split in in two lengthways and hinged on either side, but there isn't room under the engine to fold up even half an infill panel. My installation  is also a bit more complicated in that I have the transponder for my depth sounder fitted in the starboard side of the well, where it gets in the way of the infill when trying to put it in. The infill has to go in from starboard to get under my engine. But I found practice helps speed up the process. The trickiest part is fitting the infill accurately in place. You would think is is easy, but it isn't, and the panel is buoyant, which means it really has to be forced down into place.
Performance wise I really don't know. I use it because it makes the boat quieter and a bit drier. If you are really flying along in choppy water, a lot gets thrown up through the well. At low speed I don't think it makes much difference (but raising the engine does, that is a real drag). At high speed I noticed that the transom is largely out of the water and the back edge of the well is in the open air, so there isn't all that much drag. But I must be nearly planing at that point. Slightly slower and I am sure there is some drag. I'm planning to stick with the arrangement for next year, but might see if I can modify it a bit to make it more self aligning in the hole.

[Julian Swindell]

Just to make details a bit clearer, here are a few photos showing the various stages of my outboard well infiller, including what the underside looks like when you take the existing flaps off. One side effect I hadn't expected, but like, is how my outboard works. Before I could only turn it very slightly side to side, so couldn't use it for steering. The cavitation plate hit the plywood holding the flaps in place. When I removed that plywood cover and the flaps, there is more clearance so that I can turn the outboard 90 degrees either direction, which can be useful for manoeuvring around marinas etc. The copper covered lump in the bottom left of the well is my through hull transducer. The two on either side of the hole are plywood clips the cross bar squeezes under. It is a doddle to fit when there is no engine, and not when there is. I had to plane the handle down to half the initial thickness to be able to fit it in. I didn't anti-foul the infill, because I take it out on the mooring, so there is no growth on it.

[Peter Cockerton]

Julian

Thanks for the photo's it shows perfectly how you implemented the idea, it also shows that you have removed I would think totally the water flow disturbance from the outboard well opening. I understand that you removed the installed "lamellae" (again if that's what it's called) because yours was damaged, mine is ok'ish so I intend to keep mine in place but shutter of the inside to reduce the flow of water into the well and then see what that does to the boat speed.

Many thanks for all your postings.

Peter

[Simon Knight]

Hi All,

I wonder if any of you have found a method of removing the glue/gunk that is used to fit the shutters to the hull.

Guess what I am about to do ?

[Matthew P]

I'll be very glad of suggestions for an efficient safe way to remove the Laminae goop, which I suspect is Sikaflex.

On a similar adventure I resorted to a very sharp chisel and plenty of sticking plaster for me and gelcoat repair for the boat.

If anyone is thinking they might join the Turtle Club (I'm already a member, along with some much more eminent persons) they should note that blanking off the outboard well also stops water flowing out freely if the boat is swamped.  The speed of water exiting depends of course on the fit of the plate but the chances are that if the boat is swamped it will not be fast enough. Some water can exit through the sump self-bailer, if it is open, and water will exit through the rudder port in the transom but only to the height of the port. 

In my experience (all hard-won) opening the main ballast tank hatch quickly transfers the water to where it should have been in the first place - the ballast tank. However, remembering to do this and finding time to wrestle with a submerged, probably stuck hatch cover (especially if not vented) takes a lot of focus and/or adrenalin.

Matthew
BR20 Gladys

[Simon Knight]

All good points.  Is suspect that the gloop is construction glue as it is cheaper, but in the end it is a moot point.  I have also resorted to using a sharp knife to remove the stuff and as of today I still have ten fingers . 

I have not finalised my design for a plug but think that I will either include  some form of hatch or make it simple to remove in the event of an application to join the Turtle club.  On that matter I wonder if these events have been written up so that we may all learn from them.

best wishes

Simon

[Matthew P]

For capsize titillation tales see Who dunnit? thread.

Matthew
BR20 Gladys

[David Hudson]

Now the Turtle Club is a group of privileged young American ladies, who even on their backs, are incapable of improper thoughts.

[Guy Rossey]

To contribute to the different ideas, I made the installation as shown, in case excess turbulences would slow me down in a race- not the case so far- . It opens and closes well . Obviously it requires space in the well and the engine (Yamaha 5 HP) has to be fully horizontally lifted to flip the cover up or down.
___________________
Catchando Bay (BR#48)

[Rory C]

Has anyone ever considered some kind of flexible water bag that would extend over the well when inflated (with water?) on the same principle as those kids whistles that unroll in front of your face! It's one of those wild ideas that I would like to explore one day.

[Julian Swindell]

That's actually a good idea, but I think an inflated buoyancy bag (full of air) would be easier to use and just as effective, if not better.

[Rob Johnstone]

Here's another solution (?) to outboard well turbulence: I've been busy doing some rough carpentry over the winter and have made a set of "outboard" doors to pug the gap, so to speak.
See them at:

https://www.dropbox.com/s/c4tkqwgkujnh7uz/Outboard%20doors.mp4?dl=0

So far (one test sail) they seem to work quite well but it was fairly calm.

AS you can see from the vidieo, the aft part of the well has been permanently filled in (about 150 mm of it) as Julian has done with his well. The mid portion is fitted with a pair of rectangular "doors", hinged along the outboard sides by means of stainless steel tubing with matching external / internal diameter. The width and length of the opening is such that the propeller and outboard shaft column will pass through when raising and lowering the motor.

The forward end of the well is left open, with a keyhole shaped slot. The outboard shaft slides through the narrow bit of the keyhole as lowering / raising takes place and the round bit of the keyhole allows the motor to the turned to provide some thrust steerage.

The doors are opened and closed by means of control lines, lead forward either side of the engine. If they work OK, they'll be on display at Mylor (otherwise they'll have been ignominiously removed and replaced by the flaps.

There's one downside I have foreseen and chosen to ignore. If you drop something in the forward part of the well, it's gone for ever......