New Old Boat, Trailer Questions

Just bought a Coronado 15.
It was a little more worn than I thought.
I'd like to put bunks along the length of the trailer instead of 2 cradles across the boat.

What kind of wood should I use.
I tried a piece of 3/4 red oak, 6 inches wide, 8 foot long just to see how it supported the boat.
Looked pretty good, but it left the center 4 feet unsupported.
So I think I'd go to 8" wide and cut it down if it did not get a reasonable support.

Any suggestion on how to size the bunk board would be appreciated.

But first - what wood is best? I could always paint or epoxy coat for some water resistance.

Thanks

Marc

 

Well apparently not many people are interested in a trailer question.

I bought a piece of white oak, based on stiffness and resistance to decay.
Apparently white oak expands across the grain significantly, so you get issues with bonding with epoxy.
I'm going to double up the thickness at the mounting points, face bonding the boards together.
Since both pieces of wood will have the same grain direction, there shouldn't be anything stressing the joint.

 

I got a new 18' trailer for my skiff which had the bunks already installed. Usually they are pressure treated wood covered in bunk carpet. Mine look to be 2 x 6 and the bunks are encased in a vinyl sheathing with longitudinal ridges. Check Magic Tilt website.

 

Are you looking for straight or curved bunks?

 

These have to be curved.
Right now the separation between the original transverse headers is 8'.
That is too long, since the CG of the boat will not be over or behind the rear header when the boat comes off the front one.
The boat would drop in the "hole" between the headers.
But, I had a piece of 3/4" Red Oak 5" wide (10 feet) to try out the bend.
Just had one piece.
The red oak almost perfectly matched the contour of the boat. It sagged about 1/4" in the middle.
I decided this meant it needed to be stiffer.

So I'm going to move the fwd support position aft about 2' and do a test with both side bunks.
I just bought White oak , again 3/4, and each bunk will be about 5 1/2 " wide.

I had to get a new fwd support (2"x3" steel rectangle tube) because the trailer widens just after the original fwd support.
So we will see how it works when I get it installed tomorrow, and the bunk boards cut.

This whole boat looked good to start with.
But I think it has been thrown together from a lot of miscellaneous parts.
The trailer could never have launched the boat right, the tounge weight was about 200#.
I've moved the wheels fwd 5" and the boat back 12".
The rudder is not stock and could not be used.
Virtually all of the "go fast" sail controls have been removed, you can see where the screw holes were patched is you know what to look for.
Right now I couldn't lock down the centerboard - parts are missing.
The tie down for the hiking straps has been removed and covered over.
The ID plate is gone, although I have a valid title.

I do wonder what happened to this poor little boat.
I sure missed a lot - guess I was too anxious to have a boat to sail.

Lots of fun things to learn.

 

The conventional arrangement for small craft is two longitudinal bunks, ideally located under any internal longitudinal stringers in the boat. These would be PT and usually SYP or Douglas fir, depending on where you're located. Texas is likely SYP. The bunks are covered with "trailer carpet" which tends to soften the abrasion potential a bit. 2x6 is the usual choice, but on small craft 1x4 or 1x6 are often seen.

The choice of curved or angled to address deadrise is up to you, but I have a 2,300 ketch on a set of 2x6, carpet coated and curved bunks that are the same pieces of lumber I install about 17 years ago. They need to be replaced, but are still holding up. Angled bunks (tighter forward than aft) has some merit on small boats, as it helps to center the boat on the trailer as you drive it on.

 

My reason for wanting longitudinal bunks is to reduce the pressure loads over the hull.
So I need to use a curved/ flexible bunk.
My 380# boat would not really begin to bend a 2x6, and there would be a very small contact point.
Additionally the boat would not be stable, unless I added additional support which defeats the purpose.
Help me, what is PT? probably a dumb question.
Interestingly enough, the lumber yard I usually use does not carry SYP. Nor Fir.

I will probably angle the bunks. The additional reason is to contact the hull without having to twist the bunk.
My little test setup clearly shows as the bunk goes forward, it increasingly only contacts on one edge due to the hull getting narrower as the bunk contacts it.

 

PT ? Pressure treated ?

 

Yep.

 

You could place some shallow kerfs across the tops of the bunks to promote bending.

 

Use a thin saw to make the kerfs narrow and when the inner walls touch, the bend will be limited.

 

You can get 5/4 decking board if you need them to be more flexible.

 

Well I moved the fwd cross member back to 6' from the back one.
The 5 1/4" wide oak bent well and touched the hull along its whole length.
I didn't think about strapping the hull down for transport, adding some force to bend the bunks. That would mean I needed less flex.
Now I wish I could have gotten 5/4 oak instead of 4/4.
More strength would ease my fretting.

 

It finally occured to me to see what happened when I strapped down the boat.
Instead of the bunk bending, the hull bent/ deflected.
This boat has no longitudinal member to match up the bunk to. Actually no transverse framing either. Except for one flimsy bulkhead just to control flooding (I believe).

I had bought some more white oak to cut down and add 1/4" to the thickness of the bunk.
Looks like that was a waste of time and money.
Now I just need to get these properly attached to the trailer frame.

Maybe I can start on the rest of the actual boat.

 

Three layers of half inch boards, wet glued and covered with plastic drop cloth to prevent adhesion to hull, and placed on the trailer bunk supports would dry to shape of hull when hull is lowered but not strapped onto glued, still wet boards.
Or you can glue it up off the trailer if you know the required radius. The example shown is my skiff stem made of quarter inch thick layers.