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Q's on trailer bunks for a Custom 17' BW Hull
hullinthewater
#1 Print Post
Posted on 10/17/20 - 12:32 PM
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Hi all-
I am finishing up re-build of an 1987 'Trail-Rite' trailer I found in very good condition to replace my old, rusting and waaay too heavy trailer.
My hull is a custom 17 [1987 Super-Sport to non-BW CC] w/a Yam F70, after market CC, TTop and on deck 12gal poly tank.
Estimated weight near 1400#.
Trailer is 18' long, coupler to last X-member, 6'-4" between fenders; 94" width overall
MAX CAP=2370#. Obviously built for a heavier boat; square tube axle = 2-1/8". 14" wheels.

My Rebuild:
2 - 2x6 single bunks and 3 -12" TPR [Yates] tapered keel rollers.
The bunk supports locate over a 10' span and are 'inverted L' pieces welded to X-members.
I intend to use 2x6"x10' Doug Fir for the bunks.

Preface Q1: Before commiting to 'Thru-bolting' bunks, I want to load boat onto trailer temporariliy to check for bunk/hull clearances that don't interfere with boat full weight on keel rollers. To do so, I plan to fasten bunks to the brackets from below with 3/8 x 1.5" lag screws for my clearance checks. Then note bunk L/R adjustments, if any needed, unload boat and thenpermanently fasten bunks in final L-R positions with thru bolt-nuts.

Q1. Will lag screws be strong enough to fasten bunks to brackets for temporary test fit [or am I courting a minor disaster with a bunk possibly slipping out of position] ?
_______________________________________________________________________

Preface Q2: The bunk brackets on this trailer 'converge' or 'skew' to centerline about 2-3". per side; IE: the rear brackets measure about 28" L-R 'on-center' and forward brackets, about 24" L-R 'on-center'.
Since I'm going to use 2x6 bunks, I can install the bunks parallel, since the width allows me to offset at each end in opposite directions. Alternately, If I fasten bunks 'On-Center' at each bracket, they will 'taper' or 'skew' toward centerline, the same as the brackets.

Q2. Should bunks be installed parallel with each other [or is it just about neglible with a BW 17']?

Any answers, comments, guess's welcome.
Thanks for reading and input.
Joe

PS: my Personal page has trailer pics that may better describe situation

(changed to full 4 digit year per guidelines at the top of this page)


Edited by hullinthewater on 10/18/20 - 10:48 AM
 
Finnegan
#2 Print Post
Posted on 10/19/20 - 2:02 PM
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Posts: 1926
Comments: 16
Joined: 05/02/08

I have a Montauk 17' hull like yours, and use a Continental CV-7 galvanized trailer under it, which fits the boat like it was specially designed for it. You should be able to set yours up similarly if you want to. It looks like you have a good frame design.

As you know, the proper way to set this up is with all weight bearing on the keel rollers. First of all, although you have already spent money for those Yates rollers, I would not use them, as they lack necessary bending strength. They will sag in the middle under hull weight as they are only supported on the shaft at the ends, and the weight is carried in the center.
I would STRONGLY recommend you upgrade to the Stoltz rollers, which have a continuous metal sleeve across the entire 12" width, which transfers the boat load to the roller brackets with no deflection. With Stoltz rollers you MUST use SS roller shafts, well greased, to avoid bonding of roller and shaft. I would also advise the addition of an 8" roller forward, to carry the forward weight of the hull, at the first cross member. It would be easy to bolt one on.

As for stabilizing bunks, all you need are 2 x 4 x 5', mounted on last two cross members.
Anything else is overkill. I simply buy the pre-carpeted ones. Locate them so they fit against the upside down "V" in the hull bottom. This will help automatically guide the boat on to the trailer. Using these smaller, and shorter bunks, will clear up the bottom of the hull for much easier cleaning and maintenance, and less chance for launching damage and wear. I do not like pre-welded bunk brackets since they cannot be adjusted, making it difficult to transfer all weight to the keel rollers. You might want to consider the bolt-on brackets, with SS u-bolts. Pacific Trailer sells these specially sized 1/2" U-bolts.

As for lag bolts, use 3/8" x 2" in 316 SS (important to avoid rusting). Through bolting is not necessary. The 2" length is necessary for maximum holding. Both the carpet thickness, and the necessary washer and lock washer under the bolt head take up the length. You can use an extra washer or two if needed.

 
hullinthewater
#3 Print Post
Posted on 10/19/20 - 5:21 PM
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Thx Finnegan-
Didn't realize the manufacture difference. I emailed Yates before purchase [even received response fr/Yates himself] and they do have a metal sleeve that lines the inside of the roller, but it doesn't appear to project all the way thru to the end of the outer bushings. These Yates were 'blems' and less than $10 each, so no big loss. I looked at Stoltz at a local Westmarine and don't recall the steel sleeve extending to each end. I'll go back to WM and look closer.

I am using SS shafts; bought a 6' length rem from local warehouse for $6, but its 303 grade [easier to cut and drill].

Reason I chose the 2x6 lumber for bunks was to have some 'wiggle' room for the lateral adjustment if needed. That's the risk with buying a generalized fit, used trailer. Worse outcome is I add the bolt-ons later.

Yes, the most outboard position for these 2x6's will place them within an inch of the the inverted V peak. [If that makes sense]
If they work out, the 2x6's are cheaper and less effort to install than 4 new bolt-on' supports. At least with 'welded' bunk supports, they're no-maintenance.

I was concerned with the lag 'pull-out' strength, but also reasoned that any incidental load is directionally opposite a 'pull-out' force. Agreed on SS lags with locks.

Related: On my last trailer, I used zip-ties to fasten bunk carpet to the bunks; used screws & washers for each end, but zips at 12" intervals along the bunk length. By doubling the carpet on itself, the zips bury themselves and never contact the hull surface. They outlasted the carpet material.


 
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