Ctr rollers/side bunks weight distribution

[John McFarlane]

Hi all,15 foot fibreglass runabout with 70hp evinrude. Trailer has 4 centre rollers and 2 side bunks. <br /><br />Question is, should the rollers support most of the weight of the boat and the bunks merely steady the rear, or should the bunks support the rear of the boat and the rollers very little?

 

[imported_Curmudgeon]

Re: Ctr rollers/side bunks weight distribution

.. or should the bunks support the rear of the boat and the rollers very little?<br /><br />Yes. Rear rollers are for loading only.

 

[Dunaruna]

Re: Ctr rollers/side bunks weight distribution

Option one.

 

[John McFarlane]

Re: Ctr rollers/side bunks weight distribution

Well there's a quandary. 1 for each. Should I toss a coin or will others chime in to upset the balance?<br /><br />With a fibreglass boat, I have the softer rubber style rollers in the centre, not the harder style as I have been told the harder style will crack the gel coat. <br /><br />Wouldn't the softer rubbers simply squash down and chop out if they were taking all the weight?<br /><br />And conversely, wouldn't the bunks not adequately support the centre, where a lot of the weight is focussed, if the bunks took all the load?<br /><br />Or is it a balance thing?<br /><br />getting confused ...............

 

[tashasdaddy]

Re: Ctr rollers/side bunks weight distribution

i use roller bunks, and have them set up to take most of the stearn weight when it is loaded. you want to support you tramsom.

 

[imported_Curmudgeon]

Re: Ctr rollers/side bunks weight distribution

Many, many boats are supported by only bunks when on the trailer (some larger trailers don't even have rollers). Bunks spread the load where keel rollers concentrate the weight (and stress) on just a couple of points along the keel. If there's minimal weight (or none) on the rollers, weight is focussed on the bunks.

 

[jtexas]

Re: Ctr rollers/side bunks weight distribution

If the trailer was made for your boat, chances are it's designed for most of the weight to ride on the keel with the bunks there for support. <br /><br />I have a 1980 15' trihull on a trailer with three keel rollers & two bunks. Modern performance hulls that sit on bunks only - totally different construction. <br /><br />Disclaimer: This is all my opinion and I'm no expert.

 

[Bondo]

Re: Ctr rollers/side bunks weight distribution

The Only Rollers I've Ever seen on trailers that are for Anymore than Loading Guidance,.... Were on Roller Trailers.....<br /><br />Bunks are for Spreading the LOAD............

 

[jtexas]

Re: Ctr rollers/side bunks weight distribution

okay bondo, just to be clear - my bunks are carrying a bit of weight, too - but they are only about 3' long - about 20% of the boat length. Of course, about 25% or so of the total weight is on the transom - still, the front 4/5 of the boat is on 2 keel rollers. I set the keel rollers at equal heights above the trailer frame then try to get the bunks where they will contact the hull at the same time as the back roller - sort of a 3-point landing.

 

[ztim]

Re: Ctr rollers/side bunks weight distribution

It only makes sense to me what Old Curmudgeon says. Rollers pinpoint weight to one specific spot whereas bunks distribute it.<br /><br />Kind of like you would lay on thin ice to try and save a person rather walk on it.

 

[tashasdaddy]

Re: Ctr rollers/side bunks weight distribution

john read the post rollers on trailers just below this post. it will tell you an easy way to set up your trailer.

 

[Dunaruna]

Re: Ctr rollers/side bunks weight distribution

Some boats are designed for 100% keel support, the bunks are only used for steadying.<br /><br />Some boats.

 

[Dunaruna]

Re: Ctr rollers/side bunks weight distribution

Some boats are designed for 100% keel support, the bunks are only used for steadying.<br /><br />Some boats.

 

[Bondo]

Re: Ctr rollers/side bunks weight distribution

Originally posted by Dunaruna:<br /> Some boats are designed for 100% keel support, the bunks are only used for steadying.<br /><br />Some boats.

True,............But,...........<br /><br />If your trailer has Center Rollers,...... And these Rollers have the Usual 1/2" Axles,......Or even the Heavy-Duty 5/8" Axles......<br /><br />That 1/2"(or 5/8") Axle will Only Support a couple hundred Pounds,.... At Best.......<br /><br />Then That particular trailer is set up for Bunk Support of the Load..............<br /><br />IF you've got a Trailer with Center Rollers that have a 1" or Larger Axles in them,.........<br />Then maybe the Center Rollers will be Able to support a larger percentage of the Load.........<br /><br />The Big But here is,.. WHICH Center Rollers Your trailer Has..............<br /><br />I've personally Replaced,+ Repaired Many trailers that had their Center Rollers, CRUSHED by Toooo Much Load........<br />That's when all the Boat Bottom Damage occurs,...........

 

[Mark42]

Re: Ctr rollers/side bunks weight distribution

My trailer has both keel rollers and bunks. At the rear of the trailer, the boat is supported (mostly) by the bunks. Up front, the boat rests on a keel roller, and gets snugged up against a bow stop by the winch. There are 3 keel rollers total. <br /><br />To get the bunks to support the boat weight, I put a floor jack under the end of the bunk, loosened the adjustable bracket, the raised it about half inch or so. Did that on all for bunk brackets. <br /><br />So far, so good.<br /><br />I can tell you that the black rubber rollers that most trailers have will crush under full keel weight.<br /><br />The keel rollers at the rear and middle of the trailer do a good job of keeping the keel from scraping the trailer when loading the boat.<br /><br />I think it is safer to have the bunks carry the majority if not all the load at the rear, than let the boat rest on the keel rollers.<br /><br />BTW, this is an old and common topic. I have read posts on both sides for the last few years. Don't think it will ever be fully resolved. Do a search and see all the arguments for/against. It should keep you busy for a while...

 

[jtexas]

Re: Ctr rollers/side bunks weight distribution

When I replaced the front two heavy rubber rollers with poly self-centering rollers, the 1/2" shafts bent the first time - I replaced with 5/8" shafts - that did the trick. Well, at first the front shaft bent, but I discovered it was higher than the middle one - I could rotate the middle roller by hand with the boat loaded. Fixed that.<br /><br />The transom (and motor) needs the support of the bunks...if that's a little different from my initial position - I guess I've been persuaded...but I have no doubt my fiberglass hull would seriously deform without the rollers carrying the rest of the load. It flexes a noticeable amount - which I know because the cockpit had no floor until I installed one recently - and you could feel the bottom flex beneath your feet in choppy water.<br /><br />One more thought (you don't mind if I state the obvious, right?): if your rollers bind in the brackets or for some reason stop rolling, your keel will dig out a trench in a very short time, and you might start scraping the trailer frame (another job for marine-tex). Don't ask me how I know.