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Engine mount height, To be original or not ?

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SailFisher
1st Mate

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USA
62 Posts

Initially Posted - 05/03/2002 : 11:30:57

Has anyone ever had problems with the engine mount location ... height ? The original owner (short guy),had moved the holes for the mount 8" towards the sky !?! (I think it was easier for him to lift the engine.) He claims the engine was taking on water.
We had serious problems last year with lost prop bite, we own a long shaft.
We're moving the mount down tomorrow, drilling holes in the hull, Ouch ... Any advice would be greatly appriciated.

SailFisher "Catalyst"
1982 C25 STD,FK

Edited by - SailFisher on 05/03/2002 13:19:01

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OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 05/03/2002 : 12:11:40

As you probably already know, the cavitation plate should be no higher than water level, or even 1-2" below. To make this project easier, get something like a wooden yard stick (gee, do they even make yardsticks out of wood anymore?) On the motor, measure from the top of the bracket (the inside surface that touches/rests on top of the outboard bracket block) to the cavitation plate. Cut the stick to that dimension, tape it to the top edge of the outboard bracket mounting block - hanging vertical. Poiston the outboard bracket while aligning the bottom of the stick with the waterline on the hull.

Steve Madsen
#2428
OJ (Ode to Joy)

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Bristle
Admiral

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USA
834 Posts

Response Posted - 05/03/2002 : 12:30:33

Without knowing your bracket and boat's vintage, I'll offer few general comments...

If your bracket is on the starboard side (mid-80s and later), the bolts should come through above the ledge at the back of the quarterberth. That area of the transom is cored for the purpose--either plywood or high-density foam between the hull and liner. Below the ledge, you'll only be bolting to the hull (although a large backer would help). Most brackets have something like 6 mounting holes on each side, to allow some choices. You can use the topmost of each set of 3 holes (the common arrangement) to help mount the bracket lower while staying above the ledge.

If you have an older boat, check inside the dumpster to see whether/where it is cored for the bracket--or use the largest possible backing board. I plan to also use a Starboard (plastic) board on the outside of the transom under my bracket.

Your main concern is the depth of the propeller, and most importantly the anticavitation plate above it. My opinion is that the plate should be at LEAST 3" below your static waterline--the lower the better (within reason as discussed below). How deep was yours? The boat will "squat" some under power so everything will be a little deeper while under way.

What is too deep? I'd say you don't want the lower pivot point between the motor and its clamps to be immersed. If it's that low, the engine may be drowned by a following boat wake or wave while under power. Also, if you keep the boat in the water, you should probably set the bracket to a level where, when raised, you can tip the motor to get the entire lower unit out of the water. Sometimes this requires blocking the bracket away from the transom to allow the powerhead (and handle) to tip forward enough.

I'm working these things out this very weekend--with a 28" shaft Honda that should end up with the anticavitation plate 8-10" below the waterline. Wish me luck--I'll do the same for you!

Dave Bristle, 1985 C-25 SR-FK #5032 "Passage" in CT

Edited by - bristle on 05/03/2002 12:34:47

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Champipple
Master Marine Consultant

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6855 Posts

Response Posted - 05/03/2002 : 14:39:12

I did this last year and If you are doing this in the water, your a bigger man Than I.

Everyone else made some good points so I will touch on just what hasn't been said already.

1. If you have a port mount, Make sure you have space for where you want to drill your new holes! We wanted to lower ours another inch but ran out of room. (Access, as you probably know is through the quarterberth)...If your a stbd mounted motor, good luck, I can't help ya!

2. Drill your holes large, then epoxy them closed with west Sytem. Tape both sides, and inject the stuff into the tape. Then when that dries, drill your holes again!!

3. Do the yardstick method...it works wonders.

dw

Duane Wolff
"The Flying Wasp"
C-25, #401 std,sk
Chief Measurer C-25/250 national Org.
<img src="http://im1.shutterfly.com/procserv/47b2dc20b3127cce9cd2f45b211a0000004010" border=0>

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Bristle
Admiral

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USA
834 Posts

Response Posted - 05/03/2002 : 19:33:18

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
1. If you have a port mount, Make sure you have space for where you want to drill your new holes! We wanted to lower ours another inch but ran out of room. (Access, as you probably know is through the quarterberth)...If your a stbd mounted motor, good luck, I can't help ya!
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

Duane: Did you mean the reverse? (...like the OTHER starboard?) <img src=icon_smile_wink.gif border=0 align=middle>

Dave Bristle, 1985 C-25 SR-FK #5032 "Passage" in CT

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.