Best Material for Engine Bearers

[grady]

Hey everyone, I am currently searching for the best material that is both available and fairly economical. I have been seeking out local suppliers of clear verical grain fir but having little luck finding the 4X8 stock needed.

I have also requested syp also with little lucK. As I have been questioned why I am targeting these particular wood products. I find myself unsure.

So my questions are ;

Which kinds of wood are best and what are the characteristics that make them best.

I'm in a bit of a pickle..

Thanks for your thoughts.



Grady

[TerryKing]

Grady, how big an engine IS this?? Do you really need 4 by 8 Inch beams for these carriers?

Consider laminating from 2x4 stock, and epoxy protection??

[marshmat]

IIRC, the guy's running a 350 small-block.
I agree with TK that you'll have a much easier time if you laminate a few 2x4s with epoxy. You're glassing the whole mess together anyway, right? Not sure about your area, but in my neck of the woods you can get clear straight 2x4s of good quality fir at just about any lumberyard.

[grady]

Hey Matt and Terry, The motor is in deed a 350 ci sm block rated @ 320hp.

And no I really don't need lumber of that size. It's just what that boat was originally outfitted with. And not being very good with the whole engine outdrive alignment thing. I just thought that I would leave all the engineering to folks with alot more experience than I.

It may luck or good fortune but the transom cut out is almost exactly the same for the OMC Cobra ( with the exception of two additional mounting holes for the volvo ), as it is for the volvo-penta duo-prop. So if I keep the mounting hieght the same then alignment should be a smaller hill to climb.

I have no knowledge of the strength of glued up pieces, are they generally stronger than comparable sized pieces of whole natural timbers?

And yes, 2x4's are available locally. But is clear vertical grain douglas fir still the material of choice. My local lumber yards say that fir offers little or no structual strength. and is mostly used for non stress related applications.

But I don't have the information to make a intelligent disission one way or another.

thanks

Grady

[marshmat]

My local lumber yards say that fir offers little or no structual strength. and is mostly used for non stress related applications.

Hrm. Guess I'd better be worried about the 30-foot trusses in the roof of my house, which are made of a mix of spruce, pine and fir 2x4s.
Sorry I can't offer much advice on the wood issue.... I don't have much expertise with wood selection.

[grady]

like I said, I really don't have the knowlege to determine if this item pocesses the characteristics that make a good choice for this application. I too use spf wood products to build allmost everything. But I guess that alone is not a big enough endorsment. I'm just trying to make the right choices now so that I don't have to revisit this any time soon.

I can't imagine a time when I would want to take on a project of this magnetude.

Although I have repowered twice before, I am overwhelmed with this one which encludes
replacing the main tank ( 96 gals )
add an aux tank ( 56 gals )
replacing engine and stern drive
instruments and harness
replacing all thru hulls
removing all deck hardware
repainting hull sides and topsides
reinstalling all deck hardware
removing windsheild and refinishing with new glass, gaskets and moulding
remove and replace rub rail
and many more small little details

so please bear with me and my silly questions, I've given considerable time and resources to this project and as you know one step is only as good as the step before it, and this step is fundimentional in nature.

thanks Matt, you have been lots of help.

Grady

[grady]

ohh an Terryking, please see my post in the powerboat forum. I have pics of the stringers and engine bearers there. I also posted a pdf of the stringer grid from the manufacturer

thanks

Grady

[PAR]

Laminating 2x4's will not produce a stable laminate, you'll need much thinner stock (an inch, better if less).

The engine bearers need good compressive strength, excellent fastener retention and good resistance to rot. White oak and live oak make fine bearers, though are on the heavy side, which isn't an issue with your boat. I prefer live oak because it doesn't check like white and it's interlocking grain makes it really tough stuff. Up north, you'll probably have to use white.

Southern Yellow Pine can be used, so can good examples of Douglas fur (much of it is junk). Your local lumber yard doesn't have a clue about the properties in the species they sell, so take they're advice with a grain of salt (possible the whole salt shaker after the comments about Douglas fur).

On top of the engine bearers, I'd install a bracket to accept the mounts. This has been discussed with you before and several approaches can be incorporated into the mount bracket design. Through bolt when any questions of strength are at issue. When not sure through bolt anyway. This is only possible with metal mount supports, which sit atop or are through bolted to the sides of the bearer. I prefer the type that sit on top, so the fasteners aren't put in sheer against the metal bracket.

[grady]

Hey Par, What I really want to do is use the 4x6 stock of mixed grain clear douglas fir. And as you mentioned use some L angle alum stock through bolted with a nice heavy backing plate, but I would like the bolts for engine mounts welded to the under side of the angle stock. But in order to achieve this without penatrating the top of the new bearer ( which seems key ) the angle stock would have be elevated of the bearer by at least 1.5" to 2.0" which not only brings me up to the original mounting height but also allows for the bolts to run completely through the nut..

any thoughts on this idea.


Thanks

Grady

[PAR]

I would have a custom set of mounts made up to fit your bearers and block. Aluminum is pretty weak stuff so it would have to be pretty heavy material. I'd use Monel, bronze, coated mild steel or stainless (in that order of preference) for the mount.

It would sort of look like a triangular pad (the actual mount) with a upside down "U" shape welded to it's underside (with the proper mount angle and gussets) that would straddle the bearer. This would put the fasteners into sheer, but the bulk of the load would be born by the mass leaning on the bearer. Of course, it would through bolt, side to side, through the bearer.

Several companies offer adjustable mounts, just as described, many making alignment much easier and more precise.