Hull Damage from trailer

[talbot]

I switched to the Stolz polyurethane rollers (orange, semi-transparent), and found they made a difference. They are all V-rollers, going from very wide to very narrow, aft to bow. Avoid the "self-centering" rollers. Their grooves indeed center the boat when retrieving, but also shift the boat to the side during launch.

I spent a lot of time adjusting roller height and fore/aft position of the boat. I found that with enough weight on the tongue that I can barely lift it without the jack, I have pretty good towing performance while still being able to manhandle the loaded trailer and slide the boat off on a shallow ramp.

(Putting the boat way aft makes it easy to launch, but puts a lot of pressure on the hull, and also makes the trailer squirly while driving. Putting the boat so close to the car that only the jack can lift the weight puts a lot of pressure on the hitch, and makes the trailer hard to move when it's unhitched.)

[GreenLake]

I have the boat forward for good tongue weight. I don't have a jack, so I need to put my back into it when I move the trailer about. Where I do that, the grounds too uneven for the small wheel anyway...

But, rollers.

I use a V roller only for the bow roller, it's actually not a roller, as it doesn't spin. Just a rest.

All other rollers are flat with little ridges at the edge. The one thing that made a difference is a shallow V with a single notch (not the spiral one) for the last roller. On retrieving, I put that roller just about at water level. Once I catch the bow with the notch, I can "lever" the boat into alignment with the painter, no matter what angle I started out with. By the time the bow hits the next roller, the boat will be straight.

After that, the flat part of the hull comes to rest on the bunks and that prevents sideways shifts and the pull from the trailer winch centers keeps the boat centered.

For launching, I set the trailer to "tilt", so it assumes a steeper angle. (I don't drive it as far into the water). That helps the boat slide off -- still needs a push to get started, so I'm in control until that point. The flat hull in the rear prevents the transom from "digging" in, and lifts the hull off the bunks. If there's enough momentum, the boat will launch straight -- as long as nobody pulls on the painter.

[talbot]

Let's get back to trailer hull damage, the topic that started this. Some sources recommend putting almost all the weight on the keelson/CB trunk, because that part of the boat is strongest. Others say the rollers should be so loose that you can turn them by hand when the boat is on the trailer.

Anyone have actual data on this? My sense from looking at (and eventually repairing) my hull was that both extremes concentrated the weight too much on small areas, plus the boat was hard to launch. Hence my current approach, which amounts to sharing the weight as much as possible over every contact with the hull. But I'm not basing this on any real understanding of the loads involved.

[K.C. Walker]

I would think that it would take some very sophisticated experiments and measuring tools to know the exact loads placed upon the hull while trailering. The static load would not be too difficult to measure but the dynamic load for a typical trip could be very difficult. If you only trailer short distances and you drive very slowly over bumps the dynamic load might not be significantly more than static load. However, if you drive long distance you are likely to be driving quite a bit faster and if you happen to hit a significant bump at speed the dynamic load could be quite significant. This is what I worry most about. The more surface area that you can support the boat on and the stronger areas you can use for that support the less deflection a point load source would have in a dynamic load situation. Put the same amount of energy in a bullet and say a mattress, if you're hit by the mattress it does no damage but the bullet could kill you. So, I agree with you, spread the load.

The Melges 17 flat bottomed scow trailer takes an interesting approach that I've thought about trying to incorporate. Instead of using straps for tiedowns they use rigid rods to connect the trailer to the cross bracse that hold the boat. These cross braces are clamped to the gunwale putting all the dynamic load out there instead of deflecting the flat hull.
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[GreenLake]

I described my experience in some detail, because it seems that sliding the boat onto the bunks is not an issue during retrieval. (I have wider/longer bunks now than what I inherited from the PO, but they could be wider still to further spread the load). In other words, if there's an increase in friction, I've not noticed an effect.

For launching, one can either drive the trailer far enough into the water that the boat starts to float off, or, use a trailer that can tilt. Both would be strategies that would deal with any increase in friction. (In my experience, rollers do not always turn easily and they can only be serviced with the boat off the trailer - bunks are more constant that way).

There are some here on the forum who are concerned about spot loads from rollers even under the deep V section of the forward hull, but they include people who trailer across the country. Your mileage may vary - literally.

Rollers have no place off-centerline on a DS, and I'd regard them as questionable aft of the CB. While there's a remaining "crease" in the hull along the keel line, so it's not entirely a flat panel, that crease is rather shallow, whereas the forward V section is stronger, just by geometry, and then reinforced further by the keelson.

The idea is that you want to not observe "flex". If you need "data", why not walk around in your boat when it's on the trailer and have someone spot for flex (or reverse those roles). The flexing is what will damage the laminate over time.

One aspect of dynamic loads is that the distribution between bunks and rollers is different - a padded bunk has more "give" to it than a roller. It may only be a fraction of an inch, but that can change the distribution of the load.

Another way to get some "data" would be to follow in another car while you let someone drive your trailer at highway speeds (best on a section of freeway in need of repair). I've seen other peoples boats just dance on their trailers, just literally being bashed to pieces. It's tough to get an idea whether the suspension / tire pressure on your trailer is optimal and whether the straps hold down the hull well enough other than by observation while under way. You might find that revealing.

[Swashbuckley]

Interesting comments on bunk vs. rollers. I fall on the bunk side of this discussion. I plan on spreading as much of the force across as much of the hull as possible. Thus I will be floating my boat off of the trailer. I think rollers apply a stress point to the this soft hull. Opinions vary .

To stiffen the hull I am currently planning on laying down a 1/4" plywood layer from the mast back to the stern, and from the CB out to the bilge stringer. Then adding 1/2" ribs at the cuddy bulkhead, the center of the CB trunk, the stern of the CB trunk, and one 2' further back. The ribs will be tied vertically into the seat sides. The tops of the ribs will be set at a height for a level floor as low as possible. Liberal resin, fairing the hull, etc........sailing.

[GreenLake]

I assume that you are going to put a layer of glass over the plywood, for protection and strength. If you do, and the skin is substantial enough, then the plywood would act as a core only. In other words, the function would be to separate the two outer layers (hull and new, inner skin) as opposed to primarily adding strength of its own. Just happens to be the way these layered panels work. Which means, you could cut it into smaller pieces, each sealed in epoxy, which would prevent any water that manages to get in through any puncture or defect from being wicked everywhere.

If you don't trust that magic, at least cut thin strips that you seal individually. That way, in case of eventual water damage, you might limit it to a single strip. The cross ribs would take care of loads in the other direction, even if you don't add much of a skin to the plywood.

Just some thoughts.

[talbot]

In any case, post pictures!

[K.C. Walker]

+1 for what Talbot said. Vicarious fun!

[Swashbuckley]

Pics will be posted. I have been having fun documenting this project. and discussing with everyone.

[Swashbuckley]

The saga continues or maybe takes a step backwards. I thought I was ready to start building back the cockpit and hull bracing. Wrong! Note it the first photo the two fg angle beams attached to the cb trunk. They were to play a prominent role in my rebuild as a solid point of attachment to the cb trunk. I know the top surface had failed to adhere to the cockpit sole but I was sure that the adhesive and fg layer were holding it securely to the cb trunk. When I began to apply pressure to the brace to attach my new construction I was surprised to have the entire starboard brace come loose in my hand. I was then able to remove 3/4 of the port brace with my hands as well. The pictures show the tale of the failure. Adhesive was applied to less than 25% of the surface area of the brace (noted by the clean light colored spots) top or side. The fg tape was apparently applied pre resined, as it was left curled up at the edges, and was also applied over inclusions 1/2" in diameter that further ruined its adhesion. Its strength of structural support was minimal.





You can see the globs of adhesive that used to hold the angle beam to the housing in place. This was not a failure of material, but of technique. So back to the design board.

[talbot]

According to Roger's book (the bible of DSII restoration, available on this site), those L-shaped wings were not intended to attach to the cockpit sole. That's the good news. You already know the bad news. They were supposed to provide some lateral support on their own, but they didn't even do that in your case. The next time I'm pawing around under my cockpit sole, I might give my wings a tug. Or maybe I shouldn't. Who needs something else to worry about? La-la-la-la--I can't hear you. I never read this post.

On a more constructive note, I believe the DS I owners -- who don't have a cockpit sole to begin with -- sometimes reinforce the CB trunk with a triangular structure ("prism" would probably be the correct geometry term) in the angle between the trunk and hull. Check the DS I forum. Another source of support is a thwart, which is standard on the DS I, and which can be added to the DS II and III. Discussed elsewhere on this forum under the topic of rowing the DS II, or I can provide an installation procedure.

[Swashbuckley]

Lateral support? Hmmm. Interesting choice and location for lateral support. Especially since they cut out around the pivot bolt. Tells me they knew they had some design problems with the DSII.
Maybe mine was built on employee training day. Course I always thought those belt and suspender guys were a little light on support. I think I need to read that book.

[GreenLake]

Anything you can do to give your CB lateral support is good.

[Swashbuckley]

Maybe we need to clarify the direction of the lateral support we are discussing.