Attaching engine to stringers

[artemis]

Yeah, that stuff is really something. I've seen people actually fall through the floor in trailers. But there is a world of difference between that grunge and a solid timber. I think polysulfides are overkill for this sort of installation. You might actually want to get it out some day (grin).

Mike

I used waferboard only as an example of the outcome. Any wood, short of iron bark, will deteriorate to that stage if encapsulated in a fiberglass shell with a place where the moisture can creep between the silicon and the fiberglass resin (silicon does not make a secure bond with fiberglass resin in my experience and the vibration from the engine, etc. will only exacerbate this) - but if you like to build a new hull every 5 or so years, go for it!

[Lopez Mike]

Well, I take rot pretty seriously but I haven't had nearly such a drastic experience. That said, I seldom seal things in with fiberglass, either polyester or epoxy. And I can't think of any place just now on any of my boats where the resin is on all sides of any wood. I'm more of a paint person.

If every penetration was going to rot the boat, our hulls would drop to bits on a regular basis. There are about a gazillion fasteners here and there on most boats, even ones molded of glass. When I have found rot in older wood boats it has seldom been at fastenings, It's been in poorly ventilated corners where fresh water cannot evaporate.

Ventilation is the key. I have tried heat in an enclosed boat and it made matters worse. A cheap computer fan in the right place will keep things sweet.

A tip for anyone who has looked at a hunk of nice looking wood and wondered whether to finish it bright (varnish) or to paint it. If there is any chance that I will want to strip off paint sometime in the future, I first varnish it. Then paint over it. That way, I can heat strip it easily. The paint just rolls right off using a heat gun and a scraper. The varnish makes a nice filler coat as well.

Mike

[S. Weaver]

Per penetrating the epoxy barrier, I would use WEST's or System Three's info on mounting fasteners. It matters. There's a way to do it that protects the wood and facilitates ease of removing the fastener later.

With respect to mounting machinery on wooden stringers, tapped holes with machine thread studs or bolts are stronger than lags in tensile and sheer. This seems heretical at first blush, but there has been extensive testing in the wooden boat building community that favors the strength of machine threads over traditional "wood" threads in wood.

[Lopez Mike]

That is interesting. As a machinist, I have always known that when the fastener is made of stronger stuff than the tapped object, then use a coarse thread. Like when tapping aluminum, use 3/8-16 rather than 3/8-24. But I never thought that even a coarse machine screw thread would get much of a bite in common woods. Maybe in hard Eastern Maple but in fir? Also, when you use a tap, you are cutting the fibers of the wood whereas when installing a wood screw or lag bolt I thought that the fibers were just displaced and thus the wood wasn't weakened as much.

O.K., you've done it. Google here I come (sigh).

[Lopez Mike]

Very educational. I learned something tonight. And I've been a machinist for many a moon!
Sorry about the monster link. You may have to cut and paste to get the whole thing.

https://docs.google.com/viewer?a=v&q=ca ... O9Qw63_nuw

[S. Weaver]

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[mtnman]

I've alway used a self-taping threaded insert for conecting something I might want to remove to a wooden surface. Pictures here:http://www.mcmaster.com/#threaded-inserts/=g83703

[Lopez Mike]

Those inserts are great too. I just assumed that what I was gaining with them was diameter. I will still use them in soft woods or end grain.

That article I posted only referred to wood screws though. They are, of course, a tapered thread. I wonder how machine screws would compare with a cylindrical wood thread like a lag bolt or a hanger screw/bolt or a sheet metal screw?

I'm interested in some relatively delicate applications where using a wood screw or self tapper of any sort often splits the wood. Drilling and tapping would be much better for that.

[farmerden]

We keep bringing up rotting wood.Has anyone used pressure treated wood in these applications? Of course we will have to use the correct bolts or screws as this stuff is extremely corrosive! Den

[Lopez Mike]

Even with the proper fasteners, I would want to do some careful test pieces to see if any finishes or epoxy would stick to it. I have some scraps of treated 2 x 6 around here that were from marina decking and the paint seems to be sticking.

Also, there seem to be two sorts of treated lumber. Ground contact and structural. The main difference I can see is that the ground contact stuff has a bunch of weird slits or punctures. probably to get better penetration of the poison.

I'm informed that getting a splinter from this stuff under your skin is bad business.