engine bolts

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redhead78

redhead78

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Dec 30, 2009
680
jeanneau 38 gin fizz sloop Summer- Keyport Yacht Club, Raritan Bay, NJ, Winter Viking Marina Verplanck, NY
Good Morning sailors. I have a motor bolt mountint ?. I am ready to bolt down my engine,I am using 3/8"x 3-1/2" lags. Should I use stainless, or a painted bolt. I Know stainless is the correct material, are they more brittle?? Red
 
seadaddler

seadaddler

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Dec 19, 2006
5,832
Hunter 36 Punta Gorda
Not Stainless

No they are not stainless but galvinized and make sure the mounts have a good coating or they will rust,ask me about my 07 Hunter 36.
And recheck every so often the bolts may loosen up.
Nick
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,760
Canadian Sailcraft 36T Casco Bay, ME
seadaddler said:
No they are not stainless but galvinized and make sure the mounts have a good coating or they will rust,ask me about my 07 Hunter 36.
And recheck every so often the bolts may loosen up.
Nick
Click to expand
Many builders use stainless lags. I've yet to see one break. The more common failure mode is the wood core in the engine stringers gets wet or just can't handle the motor loads over time and gives up the threads.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,760
Canadian Sailcraft 36T Casco Bay, ME
William12213 said:
And that is the problem I have Mainsail. What is the best way to fix that?
Click to expand
The fix can be done a number of ways. As you found out Catalina was also famous for this rather questionable method of holding an engine into a boat..

I prefer to over bore the holes then attach stainless threaded rod to the mounts centered in the holes and held onto the mount with a nut on the top and bottom. The mounts are then mounted to a piece of 1/2" ply with hole centers that match the motors mounting holes, center to center, exactly.

You then judiciously wax the stud/threaded rod and put a nut on the bottom. Fill the over bored holes with un-thickened epoxy then remove it with a syringe. This wets out the wood. Next thicken the epoxy with coloidal silica (cabosil, Aerosil etc.) and inject the hole with this mixture until about half full. Then drop in your contraption of mounts and studs with a waxed fender washer under the bottom nut on the mount. Fill with thickened epoxy as necessary. Make sure it is aligned and perfectly centered and let cure. Once cured you can actually back the studs out because they were waxed. You now have an encapsulated nut plus about 4" of threaded epoxy. You will likely be going more than 3-4" deep and it will be very, very strong..

There are a number of ways to tackle this job but this is a method I find to work well..
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,359
Catalina 34 224 Maple Bay, BC, Canada
William12213 said:
And that is the problem I have Mainsail. What is the best way to fix that?
Click to expand
Maine Sail's way is the best. If you don't want to move your engine to do that, here's what I did.

Remove the lag bolts. Cut a bunch of toothpicks in half, round or rectangular, your choice!:)

Start to fill the holes with silicone sealant, NOT epoxy. Halfway through start stuffing the toothpicks into the hole(s). Complete the fill 'er up with silicone.

Allow the silicone to dry for no less than half an hour, or one beer, whichever comes first.

Re insert lag bolt(s).

This is NOT an elegant engineering solution to the basic problem that Maine Sail mentioned about the dumb stringer idea used by Catalina.

It does, however, stop your lag bolts from backing out (up). Which is what the problem was to begin with! (Others have used longer lag bolts to try to "find" some substantive wood left further down inside the stringer.

The weight of the engine keeps it down and the bolts carry a LOT of shear force. Some have told me: "But it doesn't keep the lab bolts down and your engine will JUMP UP!" And run away, I assume they mean. Hasn't happened yet...:dance:

Mine is a quick fix, Maine Sail's one is the real fix.

Your boat, your choice.

Oh, and to answer the POs original question: stainless.
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
The mounting bolts have to carry the thrust load and the engine torque. I would probably over bore the bolt holes and epoxy a locust or white oak plug into the hole. Essentially the same thing that Mainesail does with epoxy.
 
Ed Schenck

Ed Schenck

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Jun 2, 2004
5,802
Hunter 37-cutter, '79 41 23' 30"N 82 33' 20"W--------Huron, OH
This thread was reduced to a discussion of rotten bed rails. Redhead asked about the lag bolt metal. I have only ever seen galvanized but then I only work on old boats.

But it is true that the rails will eventually give up the bolts(screws). Since he is working from scratch maybe he could oversize the holes and epoxy in some better wood material. Then redrill for the correct size and length of lag bolt. But not too long!
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
My boat came with bronze hanger bolts for the Atomic 30. But there were only four and the Volvo required 8 bolts. I used hot dipped galvanized steel lags and after 11 years of service they are still bright. I have set up machinery using wood frames and motor mounts and you want the toughtest, hardest wood you can find under motors and bearing blocks.
 
redhead78

redhead78

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Dec 30, 2009
680
jeanneau 38 gin fizz sloop Summer- Keyport Yacht Club, Raritan Bay, NJ, Winter Viking Marina Verplanck, NY
Thanks for the info guys, I think I will use 3/8x 3" Stainless steel lags with washers, I think my stringers are in good shape. Thanks again Red
 
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