Mounting Height Of Outboard Motor Mount

[sreidvt]

Hi All,

I'm still restoring the 1974 O'Day 23 Pop-Top I bought last fall so I have not ever seen it in the water (the pic. at left was made by the previous owner). I'm installing a new (more stable) motor mount and will be moving my Honda 5 long shaft over from my Mirage 5.5. Having done various measurements on both boats it seems to me that I would want the bottom edge of the mounting block -- the block the motor clamps to -- (which is 10 3/4" tall) about 3" above waterline when the bracket is in the down position. Does that sound right? That's about where it sits on the Mirage and that seems to be low enough to prevent cavitation with the crew in normal places.

Any thoughts on this most welcome. I'm moving the motor mount over to the left side of the stern because that is going to balance the boat better.

Have already finished many projects on the 23 and will soon put the 5.5 in to sail while I keep working on the 23.

Cheers,

 

[sreidvt]

Anyone? Honda's recommendation is that the cavitation plate sit no more than 2" below the water. Yamaha says 3" or more for sailboats. Given that a sailboat can pitch a lot I'm thinking at least 4" is good. On my Mirage the plate is probably about 9" under but the idle port is still above water level.

I welcome any input here. The Mirage is a semi-planing hull while the O'Day 23 is not.

 

[Ward H]

I just happened to be recording measurements of my outboard bracket and stuff today. The bottom of the bracket sits 5" above the water and the top of the back is 18" above the water.
This is on a Yamaha 9.9 on an O'day 25.
FWIW.

 

[sreidvt]

I just happened to be recording measurements of my outboard bracket and stuff today. The bottom of the bracket sits 5" above the water and the top of the back is 18" above the water.
This is on a Yamaha 9.9 on an O'day 25.
FWIW.

Hi Ward,

Thanks very much. Those numbers are very close to what I'm thinking should work for my 23. Do you have any problems with the engine cavitating in rougher water? Does the Yamaha have a 20" or 25" long shaft?

 

[Ward H]

I have the 25" shaft model. No problem with cavitation but I have a 25 so your milage may vary.
I think my bracket is mounted a bit low because under power it the stern squats down and the bracket is touching the water.
But, I'm not about to mess with what worked for 13 years.

 

[sreidvt]

Hi Ward,

My Honda 5 has a 20" shaft so that mounting position might be just about right for this motor. The bracket also adjusts to four positions so the motor can be used up higher when the water is calm.

Thanks,

Sean

 

[rogjack2]

What seems to work well on my 23 is that with the bracket in the lowest position , the cav plate is six inches below the water level and the prop has good bite even in choppy water. Roger

 

[sreidvt]

What seems to work well on my 23 is that with the bracket in the lowest position , the cav plate is six inches below the water level and the prop has good bite even in choppy water. Roger

Thanks Roger. That's exactly the kind of information I'm looking for. Do you find that your the actual water line on your stern sits pretty close to the painted water line?

 

[rogjack2]

Hi--I used the actual water line for reference( the scum line at haul out----it was two inches higher than bottom of stripe ). Then measured to confirm my bracket travel would lower the motor to give the prop the proper bite --level, stick with reference points , tape measure, etc. I do not have much weight in storage area beneath cockpit. Roger

 

[sreidvt]

Thanks very much.