A25 motor mount repair

[johnvb1014]

We have owned a 27 for some time, and recently bought a 25 so we can be more mobile. Our 25, "Sigrid", is undergoing some extensive refitting, and I anticipate this will be first of many questions for the group. The current issue is a crack in the hollow fiberglass stringer near a rear motor mount. Sigrid had been repowered with a Beta 30 hp and the installation was pretty poor. There is a wooden timber attached to the fiberglass stringer, cut in a wedge shape to allow for the correct angle for the engine. The motor mounts were attached to the timber with lag bolts that came loose. Also, at the aft end of the wedge shaped timber are cutouts in the fiberglass stringer. Not sure if this was part of the original engine installation or an attempt to provide access to through bolt the narrow edge of the timber to the stringer. I suspect its the latter. The cutout provided a weak spot where the fiberglass stringer has cracked, resulting in a bad vibration at idle.

Attached are some crude drawings of the existing situation and a proposed solution. Sigrid is now in winter storage so I can't get photos until spring, but hope the sketches are clear. Although I suppose I could cut out the entire stringer under the existing timber and replace with one solid piece of wood, I'm thinking leaving the thick end in place will be easier and also ensure that the location and height of front mounts will be correct, and can use the angle from remaining piece of timber as a guide for the new piece. The steel plate with nuts welded on the underside will allow regular bolts to hold the motor mounts. I would attach the steel plate to the wood with adhesive and a bunch of structural screws. The replacement wood piece would be attached to the hull with adhesive (are spacers needed?) and screws through the side of the fiberglass stringer.

Any comments/suggestions would be appreciated.

Thanks

John VB

[kerrye]

You don't mention a repair to the cracked fiberglass stringer. Can it be reinforced with fiberglass layers using the existing hole as access? Alternately, a piece of wood cut to size to fit inside the stringer and slid thru the hole into place and thru bolted to the sides of the stringer? Or, a U-shaped piece of aluminum or steel slid down over the top of the stringer and thru bolted thru the sides of the stringer? Now that I think about it, perhaps the best solution is to replace your flat plate with a U-shaped plate which can be slid over both the stringer and wood wedge and then thru-bolted thru the sides of the fiberglass stringer. This would add a lot of strength and would probably obviate the need for a repair to the existing crack. The sides to this U could be triangular to match the angle of the wood wedge so that they could be straight along the side of the fiberglass stringer.

[dkirsop]

Keep in mind that the stringers also serves as air ducts to deliver air into the engine compartment. Whatever you do, make sure air can still flow into the engine compartment.

[johnvb1014]

Dkirsop, your comment on air flow is one I would not have thought about and wish I could go look at the boat to examine it from that perspective. Absent that (since the boat is in winter storage) can you describe further the air flow scheme for engine compartment on the 25? Where is the intake for the air flow and how does it exit from the ducts into the engine compartment? Thanks.

[Northern Spy]

I'm in a similar situation with my A25. After an engine swap by the previous owner, my motor mount bolts keep loosening. I would like to remove the bolts and reinstall them from inside the stringer with some sort of capture type tab possibly welded on. Then I could secure from the topside with a nylon lock nut.

I would also like to plumb my air inlet in a heavy hose directly between the intake and the aft vent while incorporating a filter. Mostly because my Universal 5424 has a pretty significant intake throb that reverberates all around the cockpit.

[dkirsop]

There are two mushroom cap air intakes located on deck behind the aft cabin. Air ducts are glassed into the transom behind the aft cabin liner and become stringers running into the engine compartment. There is a hole in the side of each stringer towards the front of the engine compartment where air enters the compartment.