First timer outboard installation

Just out of foolish stubbornness, I hope to install my own outboards on the boat I'm building.

Hundreds of pictures over at my build thread: Sea Sled Madness.

I'm looking around for a pair of good used outboards, between 115 and 250 hp. That's quite a range, but I don't know what I'll find.

I'm reasonably skilled at a lot of things, but this is new to me. What are some good resources to start with? At this point I don't know enough to ask detailed questions.

J

 

A good start would be to look at the Yamaha rigging catalog. It at least will help you see how complicated it can be....

you need to plan routings NOW

MRPCatalog 1 https://online.flowpaper.com/7c250766/MRPCatalog1/#page=3

 

Can you remind us please what the transom height is?
And perhaps post a photo of the transom here for reference (I have seen them on your other thread, but it would take time to find them).

I think that you could possibly have the two engines fairly close together, like on a 'typical' monohull - or further apart, a bit like on a catamaran.
Pros and cons (as always) of both methods - which would be the best for a sea sled?
If they were far apart, then I suppose you would have to be careful about making any tight turns, and then the outside (re the turn) engine might start ventilating (?)
Or do sea sleds stay fairly level when turning?

If a pair of two stroke engines came up for sale, would you consider them?
Or are they pretty much banned up your way now? They are still fairly popular down here.

 

Sea sleds supposedly turn pretty flat.

My first choice for engines is a pair of Evinrude 150's.

@fallguy asked me about a deckplate for bottom bolts - the things I don't know that I don't know are the big concern.

 

Some relevant pics.

 

Transom is 20" tall.

 

A good start. Routings aren't a concern at least. I won't be installing any kind of interior so the most convenient route will be easily accessible. But tell me about deck plates for bottom bolts.

 

well, the mounting bolts for the bottom of the outboard are an important thing to plan for..I didn't and what a friggin pita nightmare...

the splashwell in my boat is 7" deep, the top bolts are 2" down and the bottom bolts are 10" down and so under the splashwell and into the cleats..I had to cut an access and then cut into my glassed cleats through the 6" hole...joy and then I sealed it up and now wish I could modify the backing plate...

Bottom line is you need access 10" below the top edge of the transom for the bottom bolts..

 

For you, a plywood transom should alsobe overbored and filled with cabosil and epoxy.

So, get or make a mounting template. Drill the holes to 1/2" iirc, then overbore to 3/4", then fill from one side only until it comes out the other side...3/4" is on the edge of much epoxy and can crack, so do it in cooler weather.

You only have 8 holes. An idea for you now would be to install jackplates. They are like 150$ each for manuals. This would give you some ability to adjust; and to get the mounts done before you install the sole for 300$.

 

I have seen guys install deck plates in the splashwells, but I hate that. For you, you'll be able to build your splashwel above the mounting holes, but the sole is above the bottom bolts if you just build across..

 

If I was in your shoes, I'd add a bulkhead for the splashwell now, then only run the sole to the BH. Then a deck plate in the BH to do the work.

Also, it would be a good place to run lines, but I also hate running rigging lines into the splashwell as they tend to be like water hoses into the bilge.

 

If you can find a pair of engines with 25" legs, then you could raise the brackets 5" higher, and then raise the transom height by 5" as well?

 

Jackplates are a great idea. Then I can put in that back deck, before I even find engines. And if they are 25" legs, raise the jackplate.

@baeckmo tells me that the aerated water coming out from under the transom extends about 4-5 inches deep, so a 25" leg on a 20" transom might be a non-issue anyway.

@fallguy , the transom has no plywood. It's built up from glued and screwed lumber, then glassed as if it was made of graham crackers. And if I divide the sole with a bulkhead then loads from the transom are not carried to the monster bulkhead as effectively.

 

I'm quite surprised at the paucity of information online. Or maybe I'm just looking in the wrong place.

 

@baeckmo tells me that the aerated water coming out from under the transom extends about 4-5 inches deep, so a 25" leg on a 20" transom might be a non-issue anyway.

You will want the cavitation plate to be very close to the same height as the bottom of the boat, possibly higher if you want to go real fast.
If it is buried, it will hurt performance and cause a reverse waterfall effect at the transom, as well as increased draft.