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We have an older model Bayfield 25 sailboat, and because the…

Customer Question
Hi , We have an older...
Hi ,
We have an older model Bayfield 25 sailboat , and because the diesel has packed it in , we want to put a 9.9 4 stroke outboard engine onto the stern . What important specs and techniques do we need to be aware of ? Ellen
Submitted: 5 years ago.Category: Boat
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Answered in 9 minutes by:
9/4/2012
Marine Mechanic: Jason, Marine Mechanic replied 5 years ago
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 17,412
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Hi Ellen,

Are you asking which outboard to buy? How to mount it? Or something else? I don't quite understand what you are asking.

--Jason

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Customer reply replied 5 years ago

We already have the 9.9 merc. 4 stroke outboard , which we wish to attach to the Bayfield sailboat at the stern in order to power the boat that way . The details I'm looking for are - how to amount the bracket and motor and connect the electrical system . The concerns are in the ' already tried ' box . Thanks . Ellen

Marine Mechanic: Jason, Marine Mechanic replied 5 years ago

Ellen,

Have a look at this picture, does this more or less match your boat?

graphic

Now when you say how to mount the bracket, you simply drill through the transom of the boat, and through bolt it. Have you ever drilled a transom before? Are you looking to do this yourself, or just try and get an idea of the process before taking it to a shop? How do you plan on steering it?

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Customer reply replied 5 years ago

Yes ,

That's what it looks like . We are planing to do this ourselves - which is why I'm checking with your site so that I don't make some drastic mistake . Yes , I have drilled through a transom before . We will be steering with the tiller in the cockpit just like the boat in your picture .

My concerns are : - is the transom strong enough to take a heavy bracket with a 9.9 four stroke Merc engine ,

- how do I measure correctly so that the bracket and engine are in the right position ie . avoid ' cavitation ' ( when the prop isn't deep enough in the water ) , and also avoid interfering with the rudder while steering with the tiller .

- Are there formulas as how to do this ?

Marine Mechanic: Jason, Marine Mechanic replied 5 years ago

Ellen,

On most sailboats the transom is very thin. Usually it is just fiberglass skinned. A proper transom needs to have a wood core under (or sandwiched) that outer fiberglass skin of 2 to 2 1/2 inches thick. Is the transom of the boat that thick, with a wood core? I ask because I highly doubt it is going to be.

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Customer reply replied 5 years ago

I don't know how thick the fibreglass is . Short of cutting a hole in it , how do you determine its thickness ? Are there specs somewhere for that measurement on a 1976 Bayfield ? So , do I get a 2 inch piece of marine plywood to attach to the outside of the transom , to which I then attach the bracket ? Ellen

Marine Mechanic: Jason, Marine Mechanic replied 5 years ago

You basically drill a hole through it, with a small drill bit. And then use the bit or a metal clothes hanger to determing the thickness. That is the only way to do it, there are no specs for it. The only place that would have had the specs is bayfield themselves, and they went out of business in 1988.

If the transom is not thick enough, then you need to work with a boat builder/shipwright as far as comming up with a plan to reinforce it safely, from the inside.

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Customer reply replied 5 years ago

Ok , thanks - It needs to be reinforced from the inside of the boat . Is there a formula for correct measurement , so that everything is in proper alignment ? ie a specific part of the engine so many inches from the surface of the water , or the midline of the boat ...? Or , does this all get worked out as you go along ?

Also , am I correct in my understanding that the $ 48 covers the answer to my original question , not each interchange on email ? Thanks .. Ellen

Marine Mechanic: Jason, Marine Mechanic replied 5 years ago

Ellen,

The 48 covers it all. The only way it would cost extra is if you wanted to tip me at the end.

When it comes to boat building, there is alot that goes into it nowadays, but that was not always the case, especially back in the 70's when this particular boat was built. Now a days design is all handled by competent educated naval archetects. Back then, what looked like what would work.

There is no formula for reinforcing the inside of an existing transom, as the boat is already built. The formulas for new boats are all handled by the archtects. The rule of thumb over the years has pretty much been when it doubt, overbuilt it. Boats today still are not all that high tech. Its all just fiber reinforced plastic.

.

Now as to the engine. Engines come in different lengths. They come in 5 inch increments from 15 inches through 30. This is known as the shaft length, and is the length of the midsection (middle) portion of the outboard. On sailboats, they typically get 30 inch engines because you do want the propeller mounted as low as you can go. On normal V bottom boats, the engines are mounted so that the plate on the engine that is just above the propeller is even with the bottom of the boat. On sailboats, because the hull is a displacement hull, and not a planing hull (the hull does not ride on top of the water, it rides through it) you typically mount the engine alot lower than you would your typical V bottom. On sailboats the boat does rock fore and aft. If the aft rises to much, the propeller ventillates (catches air) and the engine overrevs.

When determining the height that your going to mount the engine, first you have to determine the boats waterline. If the boat is dirty then it is easy, as the hull will have a waterline on it. If the boat is clean, then you have to swim out and make a mark on the transom where the waterline is. From there, you typically want the center of the propeller a good 4 to 6 inches under that waterline. Much higher than that and proper will be to close to the surface, and catch air an blow out as the boat pitches.

Feel free to reply back with any quesitons.

--Jason

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