Best wood for motor bed in bilge

[J_Boat]

Hello All,

Sorry for the blasphemy, but, her hull is fiberglass and this is a forum on woodenboat.com. But,.... you guys are the ones that know about playing with wood in the water and the parts I need some help with are the wooden. See the image links below. The longitudinal members (about 12ft. long) that bolt into the hull and to which the motor cradle bolts (wooden and then a metal frame inside of that) are rotted. The way the longitudinals are bolted into the hull will tend to hold water. I will drill drain holes in the fiberglass channels that the wooden long's sit it, but, they will still likely have to put up with some moisture being retained in their seats. So, my question. What are the best options for wood to rebuild the longitudinals? Oak? Laminated plywood? Other? How should I coat them to best protect them?

These longitudinals lend stiffness to the hull and support the floor.

In this image, you can see the longitudinal running closest to you.
Inside that, there is bolted another wooden piece to which the metal engine bed is mounted.
http://ulmertech.com/images/motorbed/longitudinal.jpg

From just forward of the motor looking back.
http://www.ulmertech.com/images/motorbed/motorbed_longitudinals.jpg

From the stern looking forward.
http://www.ulmertech.com/images/motorbed/Photo_021008_007.jpg


For a broader look at the project, see http://www.ulmertech.com/j_boat.html

Any and all other comments and suggestions on/about the project are welcome.

Thanks.

PS - Is there a way to make the images show up? I work with computers for a living, but, don't see an easy way to display images in line with the post.

[Jim Ledger]

Take out the engine and everything in the way. Cut out the old stringers and grind the old glass flanges back to the hull itself. Wear a mask. Construction grade Doug Fir is as good as anything else to replace the stringers. it'll rot eventually no matter what you do because you're building a rot prone structure. The entire fiberglass boat industry has no problem with this. Neither should you. There is no alternative.Wet out mat-roving-mat pieces about 1' x 3' on a flat board and then lift up the wet laminate and position it in place and roll out the bubbles.Reassemble the boat.

Don't forget to wax the hull when you're done.:D

Good luck and better you than me, I hope to never have to do that kind of thing again.

[Bob Smalser]

Use White Oak heartwood, as that's what the originals probably were. Strong, absorbs shock and vibration well, and very rot resistant. Try to obtain riftsawn stock so those bolts don't run dead parallel to either a growth ring in one plane or a ray in the other.

http://65.13.81.113/images/motorbed/motorbed_longitudinals.jpg

The only reason the originals failed is drainage. Wood butting against metal or FG absorbs moisture as the metal sweats. Once the wood gets to 20% MC it begins to rot.

Avoid that by insulating the wood from metal and FG by bedding in felt and a good sealer like 3M 5200, and adding enough drain holes to those pockets so there is no way wood can puddle there. Same goes for the engine beds down below. They have to have enough holes (limbers) in them so water doesn't puddle long under any circumstances of trim. The same goes for the bolts. The steel must be bedded where it touches the wood or the sweating will encourage rot.

Last, probably the best treatment for your WO is CPES sealer beneath the paint to help keep the moisture below the 20% rot threshold. The a paint topcoat of course to keep the grease and oil out.

http://65.13.81.113/images/motorbed/longitudinal.jpg

[Jim Ledger]

It'll still rot eventually. The drain holes let the water in more than out and it's just about impossible to get good drainage because you've glassed the wood in and the glass you've just laid on the hull is always higher than the bottom of the stringer. The polyester won't like the white oak or the CPES, but will stick adequately to Fir.

[Bob Smalser]

It'll still rot eventually. The drain holes let the water in more than out and it's just about impossible to get good drainage because you've glassed the wood in and the glass you've just laid on the hull is always higher than the bottom of the stringer. The polyester won't like the white oak or the CPES, but will stick adequately to Fir.

The ladder braces can be fir, no problem. I'm talking the beds which are bolted, not glassed to the hull. And as epoxy sticks just fine to and is vastly superior to polyester, the last thing I'd do is add more polyester. Unlike epoxy, it's hygroscopic and will cause rot all by itself.

http://pic20.picturetrail.com/VOL12/1104763/6771586/104804800.jpg

[Jim Ledger]

Agreed on the engine beds, Bob, but glassing in the stringers to the hull with epoxy will be fairly expensive. It's been my understanding that epoxy works well with cloth but you never see it used with mat or roving. The polyester mat-roving-mat combination provides quick build-up and tremendous strength in this sort of application.

[JBreeze]

A different thought might be to present your questions and pictures at the "Repair Techniques" section of Bateau2.com.

http://forums.bateau2.com/viewforum.php?f=10

Jacques has helped several people with rebuild problems.....he wants to sell you the materials, but that seems to be a bargain in exchange for some technical advise. He has substantial knowledge of design, glass, engine size and placement, etc,

You should address the following questions from the beginning if you choose to go that route:

...will ask more questions if you decide to work with us:
- engine type
- mounts spacing between centers
- what's the condition of the other stringers? The ones forward.
- how about that transom? Is it still solid? What is it made from?

That is a neat looking boat! ... Good luck with the project:)

[Mrleft8]

Blasphemy warning! How about pressure treated SYP? Doesn't that have a 40 year guarantee?

[Jim Ledger]

For the motor mounts or stringers?

On the plus side for motor mounts, the yellow pine has a good vibration absorbing quality. Sabb reccommends a softwood mount for their diesels.

On the debit side, treated SYP shrinks like crazy after treatment. Bob Smalser probably has the figures, but if you nail 2x4's tight together on a deck, you'll soon have nice quarter inch gaps between the boards. For a motor mount, this would not be good. The wood would have to be well seasoned.

[J_Boat]

All,
Thanks for the education.

Jim, yeah, I have a demolition to do, yet. But, it appears to me that the longer outer longitundinal stringers were originally just through bolted into the fiberglass channels. I don't see any evidence of their having been any adhesive/epoxy between the stringer and the channel. I don't think I need to completely relaminate new stringer into the hull. Rather, ' get the right (or appropriate) material, cut to size, bed in something appropriate (5200 maybe) and bolt in place. Obviously, relaminating new stringers into the hull would be 'stronger', but, I think I can do at least as good a job as her original build, then she'll out live me.

And, about the 'wax'......man would that be a lot of wax. ;-) I have spent nearly no time on the outside of the hull, yet. But, she'll probably keep her work boat aesthetic.... maybe something like Brightsides polyurethane, white outside and decks with light blue or Newport Green toe rail and roof. I've redone the roof and painted it in with Brightsides and it lays down fairly well even with an amateur using a brush.

Bob, thanks for making the images show up. After some of the reading I've done including in Wooden Boat Mag., I was thinking oak bedded in something. I think there is one local lumber yard that handles a wide variety of woods and will mill it to size.

I've used pressure treated pine on the wheel house side and roof and it glues and paints well enough after it has dried. It does shrink a LOT. The ladder structure under the roof had to be disassembled and refastened after it dried. But, since then, it has behaved itself (about 2 years since).

I thought about pressure treated for these stringers, but, the larger pressure treated timbers that I can find usually have large blems (splits, checks, etc.). OK for building docks, but, not boats. So, I was immediately worried about long term strength. She'll be getting a new diesel at about 75 hp which is relatively small, but, if these stringers began to split length wise, I'd be in trouble. I'd rather have the prop spinning than the motor.

Finally, I had not even considered using something different for the engine bed. I've wondered what I could do to minimize noise, vibration, etc.... and had not even thought about using a softer wood for the bed. The bed pieces are 'floating' above the hull, just through bolted to the stringers. I figured I'd want the strongest rot resistant species available for the the bed pieces. But, something softer 'sounds' like it makes good sense. (made a pun and I'm proud enough to have to mention it ;-)

Thanks again guys.....

[Jim Ledger]

Just pulling your leg about waxing your boat.;)

Most, if not all, pressure treated 4 x 4's thru 4 x 8's are what is termed "boxed heart", which means that the heart of the tree runs through the center of the timber. Sawing in this way guarantees serious checking, from the heart out. Look for yourself. If you can find some seasoned wood, clear of the heart, then you might have a suitable timber.

The reason that I caution against using unseasoned timber for an engine bed has to do with engine alignment. As the timber shrinks, the carefully aligned engine will naturally drop and must be shimmed up and realigned. This, however, is true of any timber, to one degree or another. On the other hand, extremely dry wood might do the opposite, once put in a moist situation. Just be aware.

Let us know how it goes and good luck.

[Paul Girouard]

Most, if not all, pressure treated 4 x 4's thru 4 x 8's are what is termed "boxed heart", which means that the heart of the tree runs through the center of the timber. Sawing in this way guarantees serious checking, from the heart out. Look for yourself. If you can find some seasoned wood, clear of the heart, then you might have a suitable timber.

The reason that I caution against using unseasoned timber for an engine bed has to do with engine alignment. As the timber shrinks, the carefully aligned engine will naturally drop and must be shimmed up and realigned. This, however, is true of any timber, to one degree or another. On the other hand, extremely dry wood might do the opposite, once put in a moist situation. Just be aware.

Let us know how it goes and good luck.



Wow , you talked yourself in circle there:eek: So the woods gotta be "Just right!" well till it isn't :confused:

Yup , clear as mud:D

[Mrleft8]

Then I'd look for Black Locust, or Mulberry..... White Oak is just as good too.....But doesn't sound quite as exotic....;)

[coelacanth2]

I'd go with the black locust. Supposedly 20-30% stronger than white oak and VERY rot resistant. I pull logs downed 10 years ago during our little ice storm out of my forest floor - the bark slips off and the heartwood (Most of the remains) is still sound . We get a lot of termites here, a bit of pine left in place for a month will show signs of invasion, and they won't touch it. Occasionally carpenter ants will, but rarely. Did I mention hard?..I have seen sparks fly off my saw chain.:eek:
A fair amount of it available on the East coast. Good Luck.

[dpincus]

Anyone know of where I can get one or two black locust fence posts around Cambridge MA? The HD's and Lowes around here don't have them. Do any down the Cape have themem? For deadeyes and pins and samson posts.

[John Meachen]

If I could view the image links it would be possible to comment.I find it unusual that the rotted parts are bolted to the hull.

[J_Boat]

If I could view the image links it would be possible to comment.I find it unusual that the rotted parts are bolted to the hull.

Sorry.
The images are on my home web server and for some reason it was tangled up. I've refreshed things. If you're still up for educating this amateur, please try the links again.


As for the stringers being bolted in, I think they were 'just' bolted. Some portions of the stringers are still sound and fit their channel tightly. I can find no evidence of any adhesive or bedding material. Being built in 1954 by the Palmer Scott yard in New Bedford, Ma. she is an early plastic hull. From what I understand, Palmer Scott collaborated with Carl Beetle to build the first fiberglass versions of the Beetle Cat. The yard later got a contract with the US Army Corp. of Engineers to build these utility boats and she has what I, a rank amateur, think are some interesting characteristics. Being so early in fiberglass builds she lacks some of the more typical fiberglass hull characteristics. The stringers sit in channels that are molded into the hull and that run about 2/3 the length of the hull which is quite flexible (the hull). I'm really hoping that new stringers (added to the already new rub rails and toe rails and the yet to be added new spray rails) will stiffen her significantly. She has a Sampson post in the bow and stern and I am suspicious that the posts where the way she was intended to be lifted. Each joins into a substantial rib (the only two ribs in the hull). And, she has foam cored reinforcing running across under her bow and stern decks. 'Seems like foam cored structural members must have been cutting edge in 1954. I expected to find balsa or similar, but, not foam.


Thanks.

[Jim Ledger]

The stringers, the fore and aft wooden pieces sitting in channels, were originally stuck to the fiberglass channels. What the channels are, is multiple layers of fiberglass placed on the finished hull interior and run up the wooden stringers. The original bond would have been quite strong but over the years the glass might have let go of the wood. This would allow more flexing. Later construction methods might have totally encased the wood across the top, making a stiffer structure.

I don't think the samson posts were intended for lifting the boat, no matter how they were anchored. Use straps from underneath.

[J_Boat]

The stringers, the fore and aft wooden pieces sitting in channels, were originally stuck to the fiberglass channels. What the channels are, is multiple layers of fiberglass placed on the finished hull interior and run up the wooden stringers. The original bond would have been quite strong but over the years the glass might have let go of the wood. This would allow more flexing. Later construction methods might have totally encased the wood across the top, making a stiffer structure.

I don't think the samson posts were intended for lifting the boat, no matter how they were anchored. Use straps from underneath.

Thanks for the info. While I had my suspicions about the use of the samson posts, I would never have trusted my own craftsmanship on the new posts nearly enough to lift the hull with them. I agree straps are definitely in order.

The original chemical bond to the wooden stringers must have been relatively poor. I can find no wood failure where any wood is stuck to the inside of the fiberglass channel as the joint failed. Further, the floor cross members were similarly through bolted into fiberglass tabs. I assumed before removing them that they must originally have been laminated into the hull (chemical bond) and then through bolted. Before the demolition, I thought I'd likely have to grind down the all the tabs and re-laminate them onto the new floor members (I hate working w/ fiberglass). However, when I removed them, none of the ones that were still sound (more than 1/2) left any wood stuck to the fiberglass tabs.

Either way, I'll be using something between the new stringers and the existing channel to re-establish the chemical bond. I haven't figured out what, yet.

[sdowney717]

over time the polyester fiberglass resin will always let go of the wood.
That is why you encase the wood in polyester and cloth all around. The timber inside will be fully sheathed even though it is not fully stuck to the glass. But all the glass should remain stuck to the hull.
I like white oak but dont use red oak. It will rot quick.
If you cant get white oak then just use good quality treated southern yellow pine. If you are careful and get the bigger pieces, you can find tighter grain.

There is plenty of decent treated wood, if you look around you can find something. I certainly have been able to find some nice tight grained pieces I cut out of the large long boards. The posts are pure junk as are the small boards around here.

[John Meachen]

I have never seen an installation quite like this.It would be very unusual-polite way of saying unknown- to see large chunks of wood bolted into the hull moulding rather than encapsulated in multiple layers of glass.It is entirely possible to use structural foam rather than wood and this would eliminate the rot problem.If following this course of action,you need to incorporate some substantial pieces of steel to accept tapped threads for the engine feet.You could also use just about any wood if you take steps to prevent the ingress of water and then apply enough glass to deal with the loads imposed by the engine and if you take pains to organise bilge drainage.LEAVE THE BOLTS OUT.