Motor Mount -- Suzuki 2.5 / Cs20.3 #4 . .

[Pete McCrary]

Sailing on the Potomac and Chesapeake Bay I just have to have auxiliary power. More than just a convenience, I consider it a safety issue. But the various motor mounts offered by suppliers seem cumbersome and ungainly. So, I'm going to try my own design.

I haven't been able to find a dimensional sketch of the Suzuki 2.5 -- so I ordered the engine (that won't be needed until next spring) and made measurements. The sketch below is approximately to scale and close enough to fabricate a "proof-of-concept" model.

The Suzuki's mount has its shaft at a 5 degree positive tilt with adjustments to 10, 15, and 20 degrees. And the Cs20.3's transom has a negative tilt of about 4.5 degrees. I was concerned that those built-in tilts would be a problem. However, I think it works out OK. My concept has the motor on the starboard side and mounted at approximately in line with the side of the footwell where it meets the transom. My measurements show that the transom need only be cut 4.5" to 5" down from the level of its intersection with the starboard shear (or 5.5" to 6" down from the transom's top edge at its intersection with the side of the footwell (extended)).

There needs to be a 3.5" lowering of the deck extending forward approximately 11" to allow full (90 degree) rotation of the motor while sailing. However, if that rotation is limited to just 60 degrees, then the required modification is much smaller. A 60 degree rotation has the skeg about 3" above the waterline (and the prop above the WL by about 6").

With the bracket offset aft from the transom as shown -- then when the engine is rotated for reversing, the cavitation plate will be under the bottom of the boat. When reversed, the thrust will take out the slack in the linkage and will rotate (the top of the engine) somewhat forward.

I'm going to "dry" fabricate a proof-of-concept in order to spot any problems or errors in dimensions. Then, before DECKING the cockpit, I'll make the modifications to the transom and deck. Critical comments, suggestions, and things to look out for will be welcome.

[Jknight611]

Pete, this is how I did the motor mount, also for the 2.5 Suzuki. The piece that plugs into this socket is on a angle to get the motor more vertical. The attachment remains on the engine while in the lasserette. Haven't made it yet, but there will be a boarding ladder to plug into the transom socket when the motor is resting in the lasserette. And, true to my form, this pic is sideways!

[Ken_Potts]

Don't forget that you'll be dealing with some amount of heel so that 6" prop clearance will be less on port tack and more on starboard.

[Dnjost]

This was my solution for the 3.5hp Tohatsu.  

 

It did wind up fouling the mizzen sheet.  My solution involved a length of shockcord tied to a ring hung off the sprit to keep the mainsheet forward when slack.  So far, it works very well with not issues in lighter air.  I have photos of it on my blog.  

[Pete McCrary]

Here are photos of the final product. Also, some details of the construction.

The motor mount element is 2.125" thick, made up of one piece of 3/4" yellow pine laminated to a white oak slab made up with eight 3/4" x 1.375" pieces (from the same board) with every other piece flipped like Alan made his centerboard. The oak (grain) runs verticle to the horizontal grain of the yellow pine. The motor clamps screw against the yellow pine.

The mounting brackets are pairs of 3/4" plywood laminated to 3/4" yellow pine. The y-pine elements are outboard and the plywood inboard.

The three (below-deck) doublers are 3/4" yellow pine -- one under the transom transverse stiffener from the starboard side to the center stiffener, one each vertical doubler on each side of the (extended) starboard footwell side.

With the hardware, it weighs just under 6 pounds. I consider the mount as robust for the purpose. The hardware is 5/16" SS machine bolts, washers, and locknuts. The bracket will be well "bedded" to the transom and removable if necessary. In a later posting I'll recite specific dimensions that would allow duplication on another Core Sound 20. And, next year, sea trial results.

When I purchased the Suzuki they didn't offer a long shaft. I'm kinda glad they didn't. This forces the motor to be lower and probably less of a problem for the mizzen sheet.

There are drain holes in each aft corner of the motor well.

The mizzen sheet may be a problem, but there's really no way to avoid it except with an "inboard engine." But it should be minimal with this setup because the motor housing and tiller hug the deck (when sailing). And there are some rigging solutions as well.

Proof-of-concept mockup.

Pieces before assembly.

Pieces assembled. The side brackets are screwed (4 each side) and glued to the center element.

Moter Mount bolted to transom.

Transverse and vertices (below-deck) doublers.

Showing the minimal transom "cut out."

Engine in fully raised position. The rounded surfaces of the engine cowling and end of tiller on the deck may provide minimal interfearance with the mizzen sheet. That can be reduced further if the engine can be held at a position of about 2/3 rds raised and the prop just out of the water. We'll see during the "sea trials."