Trailer to properly support the boat.

I've been working on a lapstrake (earlier post) and now that I have the info on the scary stuff. Bending and replacing frames is going well. Now, I have to start thinking about the day she goes to water. Since it was trailer life that nearly killed her, I need to make the trailer more "lapstrake friendly". I want the hull to take some its own weight so it doesn't start to sag again (got it pretty fair, I think).

Anyone have suggestions on trailer engineering. 19', round bilge, lapstrake with long keel, and wine glass stern.

 

You don't want the trailer supports to hold up any potions of the planking if you can help it. What you want is the boat to rest on her keel and be prevented from flopping over onto her flanks with bunks or my preference are support stands. The worst thing you can do to wooden planking is push against it hard in localized areas, like bunks or supports. Never use rollers on planks either, again the same reason, point loading in a very small area, which will pop butt blocks, fasteners, clenches, etc. I can guarantee it.

If your planking is well fastened, the deck tight and well attached, the keel solid and not permitted to hog (well supported), then the turn of the bilge will resist sagging for some time. A few well placed, turn of the bilge support stands can keep them from drooping to a degree, but if drooping becomes and issue, it's not the trailer, it's something else, like loose fasteners.

The images show a trailer about to slide under a 26' lapstrake powerboat I've restored. This is why it's missing fenders, guides, forward supports, etc. If you look closely the bunks are beveled to fit the rolling deadrise in the bottom. Two of the four bilge support stands are installed. Most importantly, you'll notice the bunks seem close together. That's because this is a single screw boat and the beds are on 24" centers (pretty much a standard). This is where you want the bunks, because the keel can't hold up the boat in the aft potions of the hull. The skeg, shaft, strut and rudder prevent under keel support, so the next hard point that will not crush frames and planking are the engine bed stringers. The stands are home made and simply pivoting pads that let the bilge rest comfortably, without a hard edge pushing into the planking.

 

If bunks touch planking, make sure it is wher planks are backed by frame members. More bunks are better.

 

Since the frames are perpendicular to the planking seams, it stands to reason that bunks will hit many. The bunks above bridged 20 of the 44 frames in the boat.

As mentioned, the bunks should land directly below the engine bed stringers, which is a single screw or outboard powered boat will be 24" apart. Multiple bunks will not be any more effective then the two under the engine beds.

The real key is to insure there aren't any hard edges pressing against the planking, between frame bays or stringers. This is how you distort planking and pop things loose.

 

Thanks again

Thanks again.

I almost made a serious mistake. I've located bolster/bunk brackets on line. I'll be installing them outboard on the turn.

One thing more: Excuse my ignorance, but there is a piece of wood just below the turn of the bilge, on the bottom. It runs parallel to the keel through the broadest section of the boat only, not stem to stern. Is this a bilge stringer? approx. 1 1/4" x 1 1/4"

 

In one of your exterior photos, there appears to be a log (hunk of wood) on the planking. If this is what you're talking about, it's a rub rail of some sort. If it's inside the boat and attached to the frames, it's a stringer.

You boat is light enough to tolerate bunks at the bilge turn, but again they just keep the boat from flopping over onto her flanks and don't push up into the planking. The weight is born by keel rollers.

Your trailer doesn't appear to have enough keel rollers, especially along the forward sections. You'll probably have to make up some brackets to hold rollers, but it's not particularly difficult.

 

Bunks for a strip-built hull.

This is an old thread, but well titled so I'm going to add to it.

The first iteration of trailer my boat had a keel support with bilge bunks for keeping the boat upright on the trailer. The boat has a stub keel with an enclosed centerboard.



When I purchased the replacement, the guy selling the trailer said I had it set up wrong for a wooden boat. His idea for a trailer setup was to bunks with supports at the fore and aft ends that would "spring" to the shape of my hull and thus provide for continuous contact with the hull for an extended length. Realizing that a strip-built, epoxy and glass boat is different that a traditionally built clinched, lap-strake, the best/proper trailer setup will most likely be different, too. I am considering revamping my trailer and would like input on a proper or improved setup.

Currently, I have two bunks per side that span 4 of the 5 frames in my boat. The bunks are currently supported at the fore and aft ends and are sprung into place though they have now taken a set and I fear that I have pressure concentrations at the bunk supports. The bunks are pressure treated SWP. I am also concerned that wood that is good for pressure treating, larger growth rings and very porous, is not the best for bunks. I am also curious about the better choices of wood to use for bunks. I think the local yards have some doug fir in their larger offering. To do it right, I think it makes sense to paint the bunks before applying bunk pads/carpet. (?)

 

You're right to be concerned about the pressure points. Yes, that's me on the boat after going over a tree to get at the trailer. The mobile 100 ton crane is behind the boat.

Look at the stands, 6 legs, 3 on each side, each holding a 2x8. This works as a temporary setup, but not long term storage. This was the setup to get the puppy back to my place. The 6 towers had individual "floppy" pads installed and the single bunk boards removed, once it was in the yard.

I intentionally positioned the bunk boards where the pads would live after is was home (at the turn of the bilge, not under the boat). Also not visible are the angle stock cross braces later installed, to keep the verticals up right and not spread, as the boat leaned against them.

It's real important to let the boat sit on the keel, not the bunks or support stands. The only thing the stands do is keep it from flopping over, not to bear any real weight. I've repaired and condemned quite a few boats, because they were stored on a poorly fitted trailer and the planking got distorted.

On your boat, the stub keel can easily bear the boat's weight, so make a box or set of athwart bunks that is can rest on. Then support the turn of the bilge in a few places so the boat remains upright.

The ideal trailer setup is no bilge supports at all, just a place for the keel to rest and vertical supports that rest against the rub rail along the sheer, which just prevents the boat from flopping over. Think of how easy a bottom paint job would be, with this setup. No pads or bunks to paint around, just the bottom of the keel, which can be handled by jacking on launch day.

 

I think then that I will add a keel bunk, but also keep all of the other bunks. My original keel bunk had sides that cradled the keel nicely, but made it a bear on steep ramps. The boat would float above the sides of the cradle and if the boat wasn't centered, it would catch on one side and send the thing tipping. The newer setup has functioned much better in the recovery process. The inner bunks function as guides and primary support and the outers provide the righting moment when needed. I've not seen any adverse affects on the boat with either configuration, fortunately. The keel bunk should round it out nicely.

 

Make the keel bunk sides as tall as you can and slope them outboard, so they act as a funnel when the keel is trying to find them. A PVC pipe V in front of the keel box would do the same thing; keep the boat centered over the box, until it's pulled shallow enough to drop in. I routinely use 1.5" and 2" electrical PVC conduit for this (the electrical PVC holds up against UV and is stronger). The best setup I've devised, had two V's, one forward of a stub keel (much like yours) and one aft of it. As I floated the boat onto the trailer, the forward V would "catch" the boat and keep it centered, while traditional vertical trailer guides kept the stern in place. As the boat was pulled out, she'd settle on the trailer, with the forward and aft V's centering things, as the trailer and boat came together. Very simple, no moving parts and the PVC would flex out of the way with serious loads. Of course once the keel was on the keel box, the bilge was also supported with a couple of "floppy stands" mounted aft.