Motor mount stringer cracks - how to repair

[rasorinc]

The cracks are on the inside of the motor mounts. I would add a layer of 2 x 6,8,10 to the inside wall extending past the motor mounts as far as you can and screw them into the dry part of the old wood. Then put a cross piece in front of the mounts and behind the rear mounts real tight and screw it to the other pieces. You do not say what State you live in so try to find yellow pine or doug fir wood to do this and fire them up and have a great summer. Just make a sinple pressure box.............Just some temp insurance for you at very low cost. The left to right pieces go to the inside of the fore and aft pieces.

 

[JSL]

From the description it sounds like you are using solid wood (2 x 4, 2x6, etc). We found that even when encapsulated the moisture content can still increase and the wood expands, delaminating the frp. The cure is to fit some relief slits in the wood or use laminated plywood.
And,
- avoid sharp corners/stress risers
- line/seal any limber holes.
- if there is any load (thrust, torque, etc) on the engine don't use lag screws... unless you only need about 2 or 3 seasons. Bolt on metal mounts are much better

 

[PAR]

Most of the time encapsulated wood works well, but a lot of folks use too thick of laminations and internal stresses as well as temperature changes can break the bond line or sheathing. 1" is the max on hardwoods and 1.25" on soft, though honestly, I'll usually laminate below these maximums, just to be sure. Attempting to bond or sheath 2x stock is a guarantee for issues.

In this instance, I'd just weld up some angle stock and brace the two beds together with through bolts and backing plates. Simple, easy, no goo factor and bullet proof.

 

[rpdwyer]

Hi all.

I've added the stiffner to my stringers to make sure they don't move anymore during the season. When it's a bit warmer, I will pull the drives and check for alignment now that everything is bolted and tight.

In the fall, likely in October, I will pull the boat for the season and do the stringers then. My fix is temporary to just get me through the season and make sure I can enjoy the boat without constantly worrying if I am damaging the drives every time I hit a wave.

edit - now to clean up that engine compartment.

 

[sarscott]

Looks like your temporary reinforcing should do the job for the season....but be gentle.

And when you are ready to take care of your stringers, save yourself a ton of grief and a bunch of money and google a system called Dryboat.

 

[PAR]

I think a "Dryboat" system on a boat like this is way more than necessary. Good encapsulation techniques will keep things fine, even with the presence of some boarding water occasionally. Dryboat and similar systems are great, if you have the budget and need to dry a core or other difficult to access or dry area, but an open bilge with stringers that need to be replaced, not so much. Next year, he'll yank out what needs to be fixed, replace with new material, maybe inert ones and redo it tight again.

 

[rpdwyer]

Hi all.

This fall I am pulling both engines out of the boat to permanently repair these stringers.

While I'm good with mechanicals and house building, I've never worked with fiberglass at this level beyond simple repairs. So my question is this... with both engines removed, is this a project I can/should take on myself over the fall/winter... or does it make sense to pony up the 3k or so to have someone professionally remove/replace these motor mount stringers? I'm not at all intimidated by a challenge... I just want to hear from experts how difficult of a job this is and how easy it is to screw it up without know it's screwed up until after the engines are reinstalled.

Thanks so much.

--Rick

 

[Skua]

I would think if you have any fabrication skills and some basic tools you should be able to do it. I'm in the middle of such a project myself. For a novice I would suggest epoxy and glass, instead of poly resin.Epoxy is more forgiving, as to setup time, and less toxic, as well as stronger than poly.

 

[rpdwyer]

Any recommendation on step by step books?

 

[frank smith]

The core could be completely rotten, but you wont know until you investigate.

It an easy fix if not, and not a difficult fix if it is. I like Vinyl ester for that kind of repair.

http://www.amazon.com/The-Fiberglass-Boat-Repair-Manual/dp/0071569146

 

[Skua]

I don't think you need a book. A quick search here will turn up many threads with very good advice and pictures. A google search will also turn up lots of articles. Before jumping into your boat you could practice with some glass, epoxy , and wood, to get feel before you commit. It's not a hard repair, just a bit tedious, and definately a tad gooey, while doing the glassing.

 

[rpdwyer]

Actually I read the West System's PDF called "Fiberglass-Boat-Repair-and-Maintenance.pdf" and section 3, "Repairing Stringers and Floors" appears to be what I am looking for. Combine with with FriscoJerrets YouTube movies as well as others and it makes the repair seem less daunting. Since my stringers are engine mount and simply run from transom to fuel tank bulkhead, aside from twin engine removal (always fun) it looks pretty straight forward.

I will definitely try to remove the old ones intact as possible to template the new ones out of laminated marine plywood.

A couple of questions...

How good is the West System for this type of fix? Seems pretty popular from what I've read.

The current stringers have a 1" hole through each of them to allow water to move from one side of the stringer to the center bilge side. This is one of the two locations that water wicked into the stringers (the other being from the top of the motor mount bolts). When I redo them, what's the best way of allowing a passage way through the stringer without allowing for water to get to the wood core? Just glass it in real well... or do they make any kind of PVC drain hole that is self-sealing?

Finally, what temperatures should I do the glass work in? I usually keep my boat in the water until 11/15 and then wrap it around that same time. It's outside in the NorthEast (Connecticut). So if I am to do this project, it looks like with the West System, 40 degree's is the absolute lowest the temperature can be with 60 degrees being more the norm. If that's the case, I would likely have to come out the first week of October. 1 weekend to pull both engines. The next weekend to remove the old stringers and prep the area for the new stringers. At that point it's watching the weather to find the best few days were the temps don't get much below 60 degrees. This sound feasible?

Thanks,
--Rick

 

[SukiSolo]

The West manual is very good. the techniques are sound and I am sure you will be fine with it. The temperature is pretty critical though, although you can get away with lower temperatures than claimed. If you mix the 5:1 ratio and warm it gently until the exotherm starts slightly, then get working very fast so the resin is thin and not left in bulk in the pot. This slows the reaction and lets you work on. It will in fact cure at about 12 deg C. More of an issue is humidity and 'bloom' if this (condensation) is high.

When in doubt work in small batches, do not mix (and waste) large ammounts. Personally I prefer the slower hardeners for a longer working time. Follow PAR's advice on seeking out other resin manufacturers, although West is fine. There are a lot of very useful fillers and additives that can be employed wisely with epoxy systems. Note that any timber encased should be dry, repeat dry. Check the Gougeon test data at 5% humidity - basically the drier the wood the better for bond and strength.

 

[Skua]

I have used aeromarine and Raka epoxies with no issues. Both are less expensive than the West epoxy. Aeromarine is non blushing, while Raka has blush and no blush. I use the non blush exclusively, and in temps. down to 45 F, with no issues other than VERY long cure times. Depending on what you are doing this may not be an issue, as it my be beneficial.

You can use PVC pipe, or bore a new hole, and line it with glass and epoxy. In any event the key will be to make sure it is competely sealed up. The factories sloppy approach, is generaly the cause of most problems in smaller vessels. Economics drive the quality.

 

[PAR]

Backing up Skua's comments, all of the major marine epoxy formulations are similar in physical properties, so it's just a matter of price. Check out EpoxyProducts.com and Bateau.com for much lower priced goo's. Don't worry about amine blush or so called "non-blushing" formulations. The conditions you'll be working in will assure some blush, even with the fancier mixtures. In other words, just assume you'll have a blush and act accordingly. Wipe off any cured epoxy with a mild soapy water and a rag, dry it, then sand normally. Don't use solvents, it'll just smear the blush around. Blush is water soluble.

I wouldn't use PVC pipe for your "weep" holes. The best approach is to make them fairly over size, then back fill with thickened epoxy, covering and sealing the exposed end grain. When this is cured, drill them for the appropriate size weep (1.5" diameter minimum). They don't have to have 'glass wrapped around the hole, the epoxy will do. For what it's worth, you can't have enough weeps in most boat bilges.

If using plywood, it'll probably be dry enough right off the shelf, but if using solid wood or you have moisture content questions, anything below 15% will work, with 12% or less being preferred.

You can apply epoxy in any temperature you want. If it's cold outside, warm the work and the epoxy. Rig a tarp over the area or the whole boat and place some non-flame heaters inside it. The goo can be heated for a few seconds in a microwave. I know guys that build boats all winter in unheated shops, using epoxy, knowing it's not fully cured. They wait for the "false spring" to show up in February and drag the boat outside in the sun and let it "cook", which completes the cure. Of course, you can use the heated tent deal too, which is my approach.

The motor mount fasteners should be treated the same way as the weep holes. Drill an over size hole, fill with thickened goo and let it cure. When it is, drill for the fastener. The West System "User's Guides" cover "fastener bonding" pretty well, so have a look. A neat trick I use, is to carefully suspend a tooth pick in the center of the hole, just filled with thickened epoxy. When the goo cures, this will serve as the pilot hole for the next drill out, as the bit will follow the weakest path, which is the toothpick.