Laminating wood for a bowsprit

[CharmCityBoater]

I am getting ready to build a new bowsprit for my Hans Christian 43T. I will be making it out of Sapelle mahogany. It is 8.25” x 8.25” x 13 feet long. Since it is impossible to get a piece of timber, that large nowadays, I will be laminating several pieces of mahogany together to form the initial shape.

Question…. Should the laminations sit horizontal or vertical once installed? Vertical seems stronger but looking for wisdom from the crowd here.

Thanks

[Pauls]

The bowsprit will see basically two loads. The first is compression, from the combined loading from the bobstay, shrouds and the jibstay. The second load is due to bending forces on the sprit. I'm not familiar with how your sprit is mounted to the hull, but commonly it is fixed rigidly to the hull. This rigidity means that some of the load applied to its tip is resisted by the rigidity of the hull mounting and thus creates bending loads on the sprit. By far the greatest loads on the sprit are vertical, from the bobstay/jibstay couple. A horizontal layout of the glue lines will result in lower maximum stress being applied to those joints.

I would strongly recommend that you use a resorcinol glue for your laminations. In spite of the popularity of epoxies resorcinol is a far superior structural adhesive. Done properly, your laminated bowsprit will be significantly superior to one made of solid timber.

[stevead]

+1 for above.

If your laminates are vertical, then the joints will be subject to shearing forces, so horizontal is preferable.

Epoxy is a great adhesive and has good gap filling qualities but is prone to UV degradation.

So if using resorcinol, just make sure your laminates are evenly clamped along the length (ie. you can never have too many clamps!), as you want to avoid gaps/voids because resorcinol has poor gap filling properties. At the same time, don't overtighten the clamps as you don't want to starve the joints of glue.

If you are using multiple pieces for each layer, don't butt them together, use scarf joints, and make sure that the joints on each layer are offset from one another.

[Bowdrie]

This is a good overview of Resorcinol glue.
And yes, it wants lots of clamping pressure, unlike the physical bond of epoxy Resorcinol is a chemical bond and finely fitted surfaces are needed.
https://www.christinedemerchant.com/...esorcinol.html

[Pauls]

To add to the above, there is gap filling resorcinol. Aerodux 185 is a gap filling resorcinol which also tolerates much colder temperatures during curing. I suggest that you look up a technical data sheet on the Aerodux and then compare it to the TDS on any epoxy. There is a difference, not in short term, but in long term joint reliabiity.

[fourlyons]

Originally Posted by Pauls

To add to the above, there is gap filling resorcinol. Aerodux 185 is a gap filling resorcinol which also tolerates much colder temperatures during curing. I suggest that you look up a technical data sheet on the Aerodux and then compare it to the TDS on any epoxy. There is a difference, not in short term, but in long term joint reliabiity.

I want to second this, I've used Aerodux a lot, it's superior to epoxy as an adhesive. Plus you can order it through Amazon!

[LakeSuperior]

Over the last couple weeks I have been gluing up 5/4 x 6 clear white ash planks to be turned into canoe gunwales using resorcinol. The needed length is 19 ft and I have been making 12 to 1 scarfs. I will saw and plane these long planks into 1 x 1 inch cross-sections with the help of a buddy.

If you follow the rules you will have a good experience using this glue and it is the only glue I would use for your project.

[Bowdrie]

Originally Posted by CharmCityBoater

I am getting ready to build a new bowsprit for my Hans Christian 43T. I will be making it out of Sapelle mahogany. It is 8.25” x 8.25” x 13 feet long. Since it is impossible to get a piece of timber, that large nowadays, I will be laminating several pieces of mahogany together to form the initial shape.

So, you plan to scarf short pieces to get the length and then laminate your longer pieces together to get the thickness you need?
If so, you'll need to fashion some kind of jig that uses a router to cut the slopes on each part unless you're quite skilled with hand tools.
Getting scarfs to lie flat and true/inline across 8+ inches is not a quick job.
Once you get the 13' planks made-up you'll need at least 3 clamps per foot of length and a row down each side.
Figure on needing ~60>70 clamps minimum, you'll only be able to glue one, maybe 2 surfaces at a time, and each layer will require larger clamp openings.
If you can't figure out some "backyard" method and have to spend $$ for clamps that will open 8>10 inches, you're going to be looking at $700 to $1K just for the clamps, and you still need a gluing bench that's "tightwire" flat.
There's a reason that spar builders that use Resorcinol have a few hundred clamps.
I see that you are in Georgia?
Can it be that hard to find a nice chunk of Georgia Heart Pine?
Center cut if possible, and for less money than the clamps will cost and just shape it down.
The Ga. heart pine will make a better bowsprit than trying to laminate a bunch of Sapele.
Sapele is used by Martin to make nice guitars though.

[NorthCoastJoe]

I built one in aluminum rather than wood. I used a section of an aluminum light post and that gave me a tapered bowsprit. It was 38 pounds lighter than the wooden one and a lot stronger.

[Sailorichiban]

Aluminum is a great idea, pleasing to the eye if your mast is also aluminum.
Many advantages;
Properly constructed , does not rot.
Much stronger.
Much easier than wood to construct.
Much lighter for a given strength than any wood.
More resistance to denting than wood.
If I were you, and I had an aluminum mast and boom , it would be a no brainer.
Good luck to you!

[Bowdrie]

It's not that easy to use an aluminum tube as a retrofit.
The OP has a "traditional" boat in an HC-43.
It has real "bitts" on the foredeck and a gammon iron at the stem, and both are used to support the bowsprit.
Having to adapt a round/tapered tube to fit existing parts/hardware that were made for timber can easily lead to "Rube Goldberg" weldments and such that really look not only out-of-place but out-of-character.
Then there is the issue of all the hardware for anchoring that would have to be adapted as well as the pulpit.
Those boats have lots of really nice hardware at the bow/bowsprit that fit the design.
It would be easy to ruin the looks of the boat with a cobbled together length of pipe.
And a nice aluminum retrofit, (built by a pro with all the TIG welding,) would cost half a fortune.
And you'd still have to paint it to make it look in concert with the boat.

[CharmCityBoater]

Bow drive,

You nailed it. I already got a proposal to build an aluminum bowsprit it was over $12,000 and still did not include everything that needed to be done.

I have a very interesting question, though…

I see a lot have suggested using Aerodux. What about Smith’s Oak and Teak glue?

https://www.smithandcompany.org/OT/UsingOT.html

Phil

[Bowdrie]

Originally Posted by CharmCityBoater

…
I see a lot have suggested using Aerodux. What about Smith’s Oak and Teak

I've not had any first-hand experience with that particular Smith's product. But, I'll bet the guys over on the WoodenBoat forum will have lots of answers about it and the Aerodux.
They'll probably know what a "gap" is regarding "gap filling" resorcinol, like how big is a gap? might it be .005 or .015?
I do know that hand fitting big scarfs, using chalk to find the high spots in order to get "light tight" joints is slow and painstaking, usually involving lots of colorful language.
I'm well aware of all the good things that resorcinol brings to the table, but it is a "fussy" product and quite unforgiving of less-than-ideal conditions.
As I said in a prior post, get a chunk of Georgia Heart Pine, (or Southern Yellow Pine,) that's a bit bigger than you need.
Then get out the power plane and make a pile of shavings.
No glue. no scarfs, no having to plane the boards perfectly flat after scarfing, and no nasty chemicals or a billion clamps.
You'll save yourself a lot of drama.

[Fore and Aft]

CCB looks like lots of good timber on Facebook. I can see a bowsprit in this pile of timber.
Cheers

[Pauls]

Regarding Bowdrie's question on the gap filling ability of Aerodux 185, it is 1/16". That is a big gap.

If you're looking for accurate, professional and quality information on wood adhesives the place to go is not a forum. Forest Products Laboratory is a US government lab which tests, measures and evaluates all things wood. This is genuine science, not opinion. They do tests on a very wide range of woods, adhesives, etc and then write up reports on the results.

Engineering with adhesives is an area I work with professionally. Epoxies made for serious industrial use always specify their glass transition temperature. Glass transition temperature is the max temperature that the epoxy can see without experiencing a degradation in its strength if the epoxy is seeing any stress during this time of overheating. Most, if not all of the epoxies sold for boat use (this includes West System) have glass transition temperatures of less than 110 degrees F. There are a lot of places where a surface exposed to hot sun will exceed that temperature. And the weakening occurs every time there is a thermal cycle above the glass transition temp.

You might notice that none of the epoxies sold for marine use list their glass transition temps. Wonder why?

This thermal problem does not exist with resorcinols.* Simply put, they are the best wood glue on the market. Aerodux 185 provides a greater gap filling ability and the ability to cure in lower temparatures than most other resorcinols.