Ganging Outboards - Does it work?

But West, that lift just duplicates the 71 degree electric tilt/trim that comes standard, right?

Also, where does the engine go? That is a drawing of the steps on the transom, right? And how do I close up the hole in the bottom and keep water out of it as the motor raises and lowers?

Those were the issues I came up with last night.

 

....yes.....but you said your bridgedeck clearance is 3'.

So even if you have a 24" leg on a 9.9-which is not enough either way- you'll want the props in the water a good amount.
How far would the engine be off the water? A foot..18 inches-all the time?

Like someone said before,the engines could go up into/onto the bridgedeck into "boxes" which become seats. No need for wells into the hull.

Anyways I am out the rest of the day:it's just above freezing,the skies are blue, so the top is going down and the heat will be cranked...

 

Catbuilder

Don't get too distracted going down a lower-from-a-height path. You know that when the engine is down it needs to be well protected from waves washing over it. It's hard to visulise a pivoting system which protects the engine when both up and down and also isn't a huge lump on the back of the boat (actually two lumps of course)

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Thank you, Richard.

Your posts are always thought provoking.

My thought is to use a box, like on the Seawind catamarans... but... have that box be collapsable so that it comes up with the outboard. These would be located way up by the full beam bulkhead that makes up the aft section of the deckhouse. In other words, at the very forward part of the cockpit before you enter the deckhouse.

See this picture to see the lower portion of the box that protects outboards on Seawinds from water coming down between the hulls:




This way, they can be tucked under seating.

The Seawind style box could collapse as you pull the outboard up. As the outboard goes down, the box expands, blocking the wash coming down between the hulls.

Alternatively, I could put a half a "bubble" fairing forward of the engine and have it slide down on a telescoping track out of the same spot. The fairing would be permanently in front of the motor and would slide with the motor, eliminating the need for the box.

Those are the latest revisions I could come up with.

Something like that will have to do, as there doesn't seem to be any other way that will work and that will be easy enough.

 

I have always thought the Seawind engine to be a neat installation

I guess your cockpit is big enough so you don't need to worry about the space the two engines will take up when raised, and you can lead the steering etc away from them. It's harder to do all that on a small boat

What I always find difficult is making the hinging bracket without the engine there. You cannot make it with the engine in situ, it's just too heavy and awkward (and I've only made nacelles for 9.9 Yamahas)

But last week I did see an full size inflatable Honda outboard used as a show display. Getting one of those might help

I eagerly await to see what you come up with

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Is it going to clear the water when tilted ? Check the maximum tilt angle to decide, a long extension will make this difficult.

 

It's hard to visulise a pivoting system which protects the engine when both up and down and also isn't a huge lump on the back of the boat (actually two lumps of course)


Sorta sounds like a place to fly the national ensign to me.

The part that holds the motor would of course need to be motor mount compatible , but above the hinge line could simply be a stout varnished flag staff.

IF I were attempting this I would go look to copy a skool yard flag device.

As the kids will cut the cords for fun most skools use a simple device with a crank and gears that allow the staff to be lowered 90deg..

I have seen them in Aluminum , but it would be the simplest of all to create , once you find a suitable large gear.

FF

FF

 

I don't think I need any of that.

The design has been evolving. Look at the picture just above of that outboard mount.

I will be doing something like this. They use the regular electric tilt feature to tilt the outboard forward, pulling the prop out of the water.

My only reservation with this setup is how low those fixed boxes are that the outboard lives in. They will contact the water with a fairly small chop. This means drag.

I'm actually not sure if those boxes are high enough to only kiss the water when you are really flying through rough stuff, or if they end up sapping your performance in fairly light conditions. Any junk between the hulls in the bridgedeck area is a potential source of drag, though not until it touches the water.

So, there are now two possibilities:

1) Do just as you see in the picture above. Build a box for the outboard to live in and use the electric tilt feature of the outboard to pull the prop clear of the water when not in use. Box may be too low to the water though.

2) Locate the outboard in the same place as the box in the picture, but instead of a solid box, have a "retractable" box that moves vertically when the outboard moves. Or... a bubble that moves vertically when the outboard moves. These will work just like the box in the picture when down, but when up, would leave next to nothing below the boat to potentially catch on the water.

 

How deep does the outboard leg need to be buried into the sea to be effective ?

 

I think this varies.

If it is calm, you have to at least have the cavitation plate and cooling water intake in the water.

If it is choppy, you have to go deeper to keep the prop from aerating, even though that risks getting the powerhead wet.

It is a balance.

I think with the boxes that hold the outboards in the catamaran in the picture, they put the outboard way down, because the box protects the powerhead from getting wet.

 

What does the wave that a multi creates at 8 knots look like. Similar to a monohull with a bow wave, stern sunk and trough forward ?

 

It's not all that bad, but if you are motoring into a chop (not a good thing to do on a catamaran, if possible), that chop gets funneled down between the hulls.

To see what it looks like going into chop at higher speeds (10-15 knots?), take a look at 0:30 to 0:36 on this video. Also look at 1:54 seconds to see what 20 knots looks like under the bridgedeck between the hulls.

http://www.youtube.com/watch?v=Lp0Z1SzPJw4

The boat in this video, though bigger, has the exact same hull shape as the one I'm building. They do make very little of their own wake at 8 knots (which is why they are fast). It is mostly the open sea coming into the area between the hulls that is the issue.

 

These three photos of my 32ft Eclipse outboard nacelle may help clarify

But remember that Catbuilder has two engines, not one. And he has twice the bridgedeck clearance of Eclipse, but the engine cannot be higher off the water

Also he has said he wants a clean underside when sailing

Because it is awkward to lean down to release the "hold down" catch on the outboard I took it off and replaced it by a rope downhaul (there is also a rope uphaul) which are the ropes you can see in front and behind the engine. So there was never any need to lift the engine box cover

The ropes going port and std are taken to the tillers so when you move the rudders the engine turns at the same time.

The nacelle I used was the bow section of a 26ft catamaran. it worked well

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Ha! I should have known Richard would have already figured this out.

Can I ask a few questions?

1) How does pivoting the centrally located outboard compare with twin screws? Was the handling in tight marinas on the East Coast USA dodgy at all?

2) How reliable is your setup? Any downtime on that engine or the general setup, or did it last?

3) How do you feel about the nacelle down there? Did you feel it created any real drag?

4) Is there anything you would have done differently?

I ask because your solution has many advantages:

*Reduction in overall weight with single engine
*Steerable thrust (I am putting in hydraulic steering - adding another cylinder to move the outboard would be a trifle)
*Less time to build out

 

I have used the Yamaha 9.9 high thrust since they first came out in the mid 1980's and have been very happy with them. I used them on 35ft Banshee, 30ft Sagitta, 28ft Gypsy, 32ft Eclipse, 34ft Romany. I have motored thousands of miles with them.

The nacelle on Eclipse worked really well, the Banshee one was too flat bottomed (although still curved in all directions. Veed is better)

The only time I had a catastrophic failure was when I was hit by lightning and the engine needed a major electrical rebuild.

We went to a friends dock in an ICW canal and turned round no problem with our single engine on Romany. I attach the photo taken as we left and you can just make out his catamaran in the distance. The wake (20ft BOA) gives an idea of the canal width. Our friend said we turned tighter than a Wharram with twin engines who struggled in his canal.

I also attach a photo of a twin engine Eclipse to show you that option.

Although the Spronk charter cats of the 70's used one big single outboard I think you'd be better with two.

Richard Woods of Woods Designs

www.sailingcatamarans.com