Any boat mechanics in here?

I can't be the first/only one to have a problem with motor mount lag bolts. I am rehabbing an 84 Shamrock, straight inboard. For some reason the motor mount lags were all loose, as in only one of eight actually needed a wrench to remove them when pulling the motor. Now it is (past) time to re-install and I am unsure what to do to prevent this happening again. I was planing to bore out the holes and fill them with thickened West epoxy, then redrill but my testing hasn't been too positive as far as screwing lags in and feeling confident in the holding power. A friend suggested boring out the holes, filling and inserting the bolts before the epoxy sets. So far this shows much better strength but I worry about how it will hold up when I need to re-power in the future. I have considered cutting the stringers down and laminating in a piece of stainless bar stock which could be threaded for machine bolts but it is a lot more work than I prefer to do.
Is there a "Standard" version of this repair that I am overlooking?

Bruce

Well, you have to evaluate the stringers and see if the wood core is rotten. Were the lags all rusty when they came out? you may need to replace the stringers themselves. Encapsulated wood rotting is common.

Lags are stainless so not much rust especially considering that this boat spent 26 years in FL. Wood doesn't seem soft, I don't know how long it ran with the lags loose, maybe since it was re-powered in 96. The "structural" damage appears to be limited to the lags vibrating in the holes and the mounts vibrating against the stringers. I am planning to fair the (shallow) indentations from the mounts moving and glass over to get a fresh surface. The plan is to return the boat to FL and keep it there rather than tow it back and forth annually. I am torn between trying to do everything I can think of now so that it doesn't need to come home for repairs again and keeping the project "simple" enough that I don't loose sleep everytime the weather liars mention hurricane. The original plan was put on new manifolds and keep the project cheap in case it dissapeared with a high tide.

Bruce

if the mounts have moved around to the point of the logs are indented, then most probably the engine is now out of alinement. you better inspect the drive line for signs of wear. and plan on spending a fair amout of time to reistall the engine in alinement. as for lags backing out because of vibration, the simplest thing would be to tie-wire them tight

if the wood isn't rotten, just "wallered out" from the loose lags, then Marine-Tex is a good idea. As an alternate/upgrade, maybe fabricate (or have it done) a U-shaped steel bracket with tapped holes in the top to accept machine thread bolts through the engine mounts. Cross bolts through the stringer to secure the U bracket. All sealed up with super duper marine caulk. Eternal.

Just bolt angle iron horizontally through the stringer (make them long to spread the load). Then have bolts or studs vertically to the mounts. You will just have to chase out a bit of timber for the bolt heads.

agree with all that was said above.

If the stringers are punky, you are just epoxying to shitty wood. Can you seat a lag without the motor and will it hold?

When I worked for Lyman-Morse, they would epoxy in 1/2" plate into the stringers to land the mounts on. Tapped for bolts, bombproof.

The alignment is going to be difficult especially if there was movement. Here's an easy way. Well sorta easy... Scoot the trans output coupling close to the shaft and then use a feeler gauge all around it to get a good mating. You also want to verify that the shaft spins easily in the stuffing box and cutlass bearing before taking too much time aligning it. It will also dictate where the motor needs to be X-Y before you spend too much time with the motor mounts.

I'd drop the motor in there, find out where you need the new super mounts to be and then worry about how you are going to slam it down for good.

For a 24 shamrock if its just a fishing boat, no real offshore stuff, you may want to try the epoxy first. Any chance of winding in a bigger lag by drilling out the mounts?

Go around with a scratch awl and poke the stringers, and the floor boards.

You're in the time frame for rotton stringers, and rotton wood. Its usually plywood of some nature with fiberglass over it.

Poke around, see if you find softness. If so evaluate what you want to put into the boat.

I am heading out with an awl to do some more investigating. The Shamrock 20 has almost no wood, seems to be the engine beds and an unfinished shelf under the console. I kind of wish they had used some in the decks because the other project is to re-attach the console and T-top that were screwed to the deck and have for the most part wallowed out the holes. I have tried using thickened epoxy before (my Sisu) to get a new surface to hold worn screw holes, wasn't very successful.
Back to the subject at hand, I do plan to upsize the diameter and length (on the ones with room) of the lags. I like the angle iron idea but am concerned that if I reduce the space available the engine might not fit back between the mounts or it might be too high to line up with the shaft. Both are things I should have thought to check on before removing the engine and disassembling the mounts. It shouldn't be too hard to "mock up" except that the mount castings are out being powdercoated and I would really like to get any needed glass work done over the next few "warm" days.
Guess there is no "Magic Potion" that I could mix up and pour in to make the existing holes hold threads.
Thanks again.

Bruce

Good info above !

Also ask here.... Shamrock Owners site.

http://www.fishtheclassic.net/forums/

or google

The Hull Truth .... another boating forum

I have tried to sign in there before. I can not answer their "Random Question"

"In the NFL, the Carolina (_____) represent SC & NC?"

Nor do I gave a rat's azz what the answer is. I love bikes boats and guns, couldn't possibly care less about any group (or individual) chasing a stupid ball!


Bruce

OK, spent some time in there today,

Longer lags will bite substantially - at least in the holes I tested. I can go an inch longer for the front mounts but only a 1/2 inch longer for the rear so I wonder about the long term durability. Playing with an awl shows that the top wood right at the hole could be better but I can't penetrate much at all beyond that with hand pressure.

When the boat was repowered (96?) something must have already been loose because there is a little filler and resin in and around the holes. The loose (since then) mounts wore pretty well into what appears to be a single layer of mat on the stringer top.

Pulling my head out of the sand I think that the right answer (so as to not have to address this again) is to fit angle iron onto a bedding of thickened epoxy and lag it in place (new hole locations) then tap holes to bolt the engine mounts into place.

3"x3"x33" angle will fit fine, I can get it in 3/8" aluminum 6061 for $20 each or 3/8" stainless 304 for $88 each. I am thinking that the increased difficulty in drill ing and tapping the stainless would be offset by it's hardness resisting wear. I wonder if 3/8" thick aluminum is sufficient for holding the threads. I can get 1/2" in aluminum but only by going to 3 1/2"x 3 1/2" which may (will just don't know how much) require some cutting or grinding to fit.

I am cheap by nature but the difference in price doesn't matter to me if it works better/longer.

Thoughts and opinions being actively sought!

Bruce

Your first thought was the best. Overbore your holes, fill with West Sytem, and then redrill. Setting your bolts in the epoxy before it sets is not unheard of either... that's how they set bolts in concrete after the fact.

If your stringers are glass over wood, the wood does not serve any structural purpose. Don't go ripping out your fiberglass if you find rot underneath. Now if your stringers are just plain wood, and they're rotting....

Fishtheclassic is a good group, as well as its sister site, ClassicMako.com. A lot less BS than TheHullTruth. I once drove a thousand miles to help a CM forum member I'd never met put a Brazilian Walnut deck in a Shamrock 20.

The second paragraph is false. The encapsulated wood IS structural.

Might think about glassing in stud bolts.

I've seen this done as a crutch.

I've also seen people use a hole saw and remove a plug from the stringer around the holes. Usually that's the softest stuff anyway.

Then they get a dowel that diameter, set it in there with epoxy, fix a fiberglass patch over it, and drill for their lag screws.

Usually on a boat with glassed wood stringers the wood is structural, and also deadening.

The first ~10 years of full composite stringer boats they were extremely rigid over the waves and very harsh. A few companies capatilized on that to stay with wood stringers, and only went to composite once they had engineered a more dampened stringer system.

Since your awl test was pretty positive I wouldn't get too crazy. Drill out some punky wood, fill with the epoxy, drill and set. And I bet if you have a problem with them again its time to find a different boat anyhow.

It doesnt need to be aluminium or stainless. Aluminium wont hold a thread under load, it is too soft. Plain old steel is fine. Pre drill all the holes and paint with etch primer and epoxy enamel. Before you install, insert bolts upside down (heads under)to match the original position of the lagscrews. Otherwise you can just weld nuts on the steel and arrange jacking bolts. Remember to seal any exposed timber, to keep the bilgewater out of it.

After much deliberation, I decided that while just reinforcing the existing holes would probably be fine, I was not confident that it would stand up to an engine replacement in the not too distant future (presuming that I end up liking the boat enough that it becomes a "keeper"). The order has been placed for two pieces of 3"x3"x 3/8" stainless angle. I will bore out any wood that appears soft and replace with thickened epoxy then bed the angle in same while lagging it in place in "virgin" locations.
I liked the idea of setting bolts in epoxy to become studs, also the idea of welding nuts or studs to the angle before installing. If/when the boat gets repowered it is very likely to be changed from a pleasurecraft (Ford 302) to some form of chevy (small diesel is another option?) and the new mount locations will probably not correspond. Yes the idea that the next engine using different locations does conflict with my concern about being able to use the same holes - what can I say, sometimes I end up thinking myself in circles.

I really do appreciate ALL of the input, Thank You. Now if I could just answer that football(?) question perhaps I could sign on to the Shamrock Forum and leave this one to more important (bike) stuff.

Bruce

Be sure to use grease or nevr seez on the threads,stainless has a propensity to gall. I'd recommend common plated steel bolts.

i had the same boat some years ago and saw the same problem at the motor mount bolts. in the case of my boat, the wood stringers were starting to go where the lags hadn't been sealed originally. i used Git Rot, a liquid epoxy, at the bolt holes. it's surprising how much can be poured in there where the wood is bad. went one size larger in SS lags and bedded the whole works with 3M. fixed.

the 20 shamrock is still one of the best looking CC out there.