Trailer Bunk spacing and fitting

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Trailer Bunk spacing and fitting

Postby Tipster1 » Tue Sep 15, 2020 8:25 pm

My 45 yo Lil Dude trailer broke it's back. It snapped right where the tongue is locked in when not flexed for launching. (same day as CB got stuck and motor overheated and quit). I considered replacing tongue for about $100 plus my labor of drilling and adding pivot reinforcement and hitch coupler and then paint. Neighbor looked askance at tires and springs.

OR just get a new trailer.

Since this is a once in a lifetime DIY setup I plan to try to duplicate old setup which adds a wide 12" guide-on center roller aft and one keel roller to support CB in addition to supplied front keel roller.
Since I have options, should I duplicate the 40" bunk spacing or go wider should I go wider or narrower?
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Re: Trailer Bunk spacing and fitting

Postby GreenLake » Tue Sep 15, 2020 11:31 pm

Rollers. I think I have one more roller in the mix, an aft one with a notch (but not the spiral one, if that's what a "guide-on" is, I only need to trap the bow in a simple notch in the center of a shallow V). Then I have three rollers forward of that, one of which is below the CB. My aft roller is dropped a bit, so once the bunks support the rear, there's no weight on it, as the "keel" in the back is not as strong as from about the CB forward.

Bunks. Some people have basically done full-width bunks. I inherited some that I thought were a bit too short and narrow and made them wider and longer (they now extend to almost the transom). I would make them no less than 8" wide if I were to do it again and wouldn't balk at 12". For a DS1, I would make sure the bunks are under the flat part of the hull and that they support the hull along the line where the seats meat the bottom. Because of the seat wall, that's pretty stiff in the fore-aft direction. Too narrow a set of bunks might still give you some flex athwartships, going wider would reduce that. Make sure to use some cover that's nice for slipping the boat off and on.

As for how that translates into spacing on the bunks in inches, I would have to measure - but so can you. So I'll pull the old "left as exercise for the reader" stunt :)
~ green ~ lake ~ ~
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Re: Trailer Bunk spacing and fitting

Postby GreenLake » Tue Sep 15, 2020 11:37 pm

PS: my retrieval technique is to not break the trailer but submerge it just enough for the rear roller to be ~at the water level. I shove the boat to help the bow over the roller, use the painter to lever the boat left-right until aligned and then pull sharply to where the bunks almost engage. I winch the last 6-8 feet up onto the bunks. Ever since I reduced the aiming to getting the bow into that first notch, I've never had the boat load askew.

For launch, I don't drive in quite as far, and break the trailer so the boat slides off at the steeper angle. This one can go wrong if anything pushes or pulls sideways at a critical moment (wake, someone pulling on the painter). "wrong" means the bow will "derail" from the rollers and get a nasty scrape on the trailer frame. But if the boat can gather momentum undisturbed it's usually fine.
~ green ~ lake ~ ~
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Re: Trailer Bunk spacing and fitting

Postby Tipster1 » Wed Sep 16, 2020 7:30 am

Thanks, GL. Humor appreciated :D
Unless someone advises otherwise I'll duplicate, as best possible, the bunk spacing from original trailer. They were 4" x 48", 40" apart. New trailer has 4" x 60" and allows me up to 59 apart. Is wider any better :?:

I plan 12" guide-on keel roller at aft end of trailer, one to support the aft end of CB and one in the under mast step. Sound good :?:

I have mixed feelings about side guides. They are on current trailer and help with confirming the center, but always seem to be in the way when I am puttering. That will be decision later.
As you probably can tell, I like to get things just so and feel sorry for people who aren't well tuned. Once you're underway, it's too late. They suffer needlessly. On the windsurfing beach, I see my mission to keep people from sailing improperly rigged and tuned sails. Hence my "handle".
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Posts: 155
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Location: PA/NJ

Re: Trailer Bunk spacing and fitting

Postby GreenLake » Wed Sep 16, 2020 1:21 pm

4" bunks are too narrow in my view (and that view is shared by many here). I've widened mine already and my only regret it that I didn't make them a couple inches wider.

On my trailer, the bunks were easy to modify because they consisted of a flat board, covered in carpet and screwed to a metal U-channel. All I needed to do was swap the board against something wider. Some trailers seem to have something like a 4x4 held up by two brackets. To change that into a wider support might mean adding a flat board on top. The DS hull really doesn't like to be supported in a narrow area.

The 60" sounds good, definitely better than 48". if the flat area of the hull is longer, you can let any added wider board also overhang a bit front and or aft. (I added a substantial overhang aft - hey, any increase in bunk area reduce the point loads).

On the question 40" vs. 59" I gave you you my best answer already. Ideally, your bunks need to be directly under the place where the seats connect to the hull (if you have a DS1 with molded seats tabbed to the hull). The lineup won't be perfect as the seats angle in a bit towards the back. I believe at the CB they would be about 32" inches apart (but you should verify that, I don't even have my boat close at hand as I write this). That would seem to indicate that with a bit of a wider bunk than your 4" a spacing of 40" would get you close. Also, mine tilt in to meet the angle of the hull, making the distance between centerlines of the bunks a bit less than the distance between supports attached to the trailer.

Mine are set up to within the limits my old trailer supports, but I can't give you that in inches. However, I was looking for something else on my PC and stumbled on this photo:
2798
which shows my trailer positioned for retrieval. The trailer is a touch narrower than the 6'3" beam of the DS, so you might get some "measurements" off that picture :).

You can see how I drop just the aft roller down to water level. I found that if I force the bow to roll on, it keeps the boat aligned until the bunks start lifting the back (the front is steeper and sits between the bunks on the rollers). Aft roller is dropped an inch or two so that the trailer can sit that much higher (and the bunks will engage a bit earlier) and also so that there's no load on it while driving. Took me a while, and many botched retrievals to figure out that this was the way to go.

After these tweaks, I can positively state that additional guides would add nothing to may setup. Any guides work best, I think, if your retrieval mode is set to "float on", not to "roll on", something I use with a different boat / trailer combination.

(Oh and nobody ever needs to get in the water).

Good luck with getting yours set up to satisfaction!
~ green ~ lake ~ ~
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