How much load on rollers & bunks?

[Azlo]

I just finished this trailer. but as you can see I need to adjust my keel & bunk rollers. Is there a process for this or just sit the boat on. I read that the bunks take most of the weight? if so how much percent weight should they take?

I know its not rocket science, right?

 

[ezmobee]

Re: How much load on rollers & bunks?

Oh crap, now you've gone and done it. This topic always seems to stir controversy and the gnashing of teeth. In MY OPINION....the bunks should support the vast majority of the weight the rollers are there more as a guide.

 

[sasto]

Re: How much load on rollers & bunks?

I know nothing about trailers but the Admirals boat sits 100% on the bunk rollers......I'm waiting for answers too.

 

[Frank Acampora]

Re: How much load on rollers & bunks?

Logic dictates that the bunks be located under or very close to a strake on the hull bottom where there is an internal hull stringer, or at the hard chines if the hull has them. This is the area least likely to deform from pressure and since there are many more rollers on the bunks than on the keel, the unit pressure is lower. Thus, even though the keel may also have a stringer, to prevent deforming, the keel rollers should only guide the keel onto the trailer and slightly support it.

You would set the bunks, set the boat on the trailer, get under it, and manually adjust the keel rollers so they have a small amount of pressure against the keel. At least, that's what I would do.

Yeah, I know--I'm arguing logic on a forum-- not a good choice LOL

 

[superbenk]

Re: How much load on rollers & bunks?

I think Frank is right on.

 

[Azlo]

Re: How much load on rollers & bunks?

Thanks everybody, im gonna go ahead try it this week end.

 

[sasto]

Re: How much load on rollers & bunks?

I'm going to adjust mine too. At this time the bunk rollers are on the stringer but the keel rollers are no where close to the keel.

 

[gozierdt]

Re: How much load on rollers & bunks?

If you look at the keel of most of these modern fiberglass boats, there is no large strength member sitting/supporting the keel. You can see that in all of the restoration threads below, if you look at the pictures as they deconstruct the bottom framing. The stringers are typically a foot or more to each side. Granted, there is some strength from the "fold" in the bottom at the keel (the 19-20 degree deadrise angle), but I agree with the camp that the bunks should support most of the weight. On my boat, I have four bunks, the longer, inner set next to the bottom strake, and an outer, shorter pair out right next to the outer strake.

 

[JimS123]

Re: How much load on rollers & bunks?

Did anybody even look at the pics before they described the all-to-common bunk / roller adjustment scheme?

This trailer has "Roller" bunks, not carpeted bunks! I would think that some of you would modify your opinion if you knew that.

If you google the question you will find responses from sevaral boat trailer manufacturers. Here's one:

http://www.thuletrailers.com/advice-a-guidance/boat-trailers

BTW beautiful trailer. Nice job of setting it up. You should launch and retreive like a pro!

 

[gozierdt]

Re: How much load on rollers & bunks?

I saw the pictures, and as an engineer, I'll stand by my original opinion- the bunks should support the majority of the weight on this trailer. There are 5 rollers per side, 10 total, versus 4 keel rollers. I'd put 50-60% of the weight on the rollers- and I'd be very careful to the the transom very close to the rear roller. The roller bunks should be put under the stringers, or as close as strake placement allows.Modern boats are typically quite stern heavy, it's imperative to support the transom very well. And the keels are not built like wooden boats were- the keel members were heavier, and there were frames crossing the bottom every 1- 1 1/2 feet. So the keels were stronger and much better supported. Even then, I support my wooden boats with bunks under the stringers, and put the majority of the weight on the bunks. Never had a hooked or rocker on my boats.

And I agree that you did a masterful job on the trailer, very nice!!

 

[Azlo]

Re: How much load on rollers & bunks?

SO should the bunk rollers be placed under the stringers or the strakes?
Im learning alot.:redface: thank you all.


Thanks Gozierdt

 

[tboltmike]

Re: How much load on rollers & bunks?

I saw the pictures, and as an engineer, I'll stand by my original opinion- the bunks should support the majority of the weight on this trailer. There are 5 rollers per side, 10 total, versus 4 keel rollers. I'd put 50-60% of the weight on the rollers- and I'd be very careful to the the transom very close to the rear roller. The roller bunks should be put under the stringers, or as close as strake placement allows.Modern boats are typically quite stern heavy, it's imperative to support the transom very well. And the keels are not built like wooden boats were- the keel members were heavier, and there were frames crossing the bottom every 1- 1 1/2 feet. So the keels were stronger and much better supported. Even then, I support my wooden boats with bunks under the stringers, and put the majority of the weight on the bunks. Never had a hooked or rocker on my boats.

And I agree that you did a masterful job on the trailer, very nice!!

How do you determine the load distribution between bunks and rollers?

 

[NSBCraig]

Re: How much load on rollers & bunks?

Did anybody even look at the pics before they described the all-to-common bunk / roller adjustment scheme?

This trailer has "Roller" bunks, not carpeted bunks! I would think that some of you would modify your opinion if you knew that.

If you google the question you will find responses from sevaral boat trailer manufacturers. Here's one:

http://www.thuletrailers.com/advice-a-guidance/boat-trailers

BTW beautiful trailer. Nice job of setting it up. You should launch and retreive like a pro!

Do you think your the only one that can see a picture?

Sorry but stupid post!

Of course we can see they are roller bunks and no that will not change anybody's mind about how to setup a trailer.

AS noted above (ezmobee) it was expected to see that link yet again and their is another one too.

Does this change anything? NO!

Just cause it's on the web doesn't make it true and just cause a manufacturer says it doesn't make it true.

How about just offering your opinion (what it is) and kill the stupid attitude dude.

Logic IS a difficult thing to argue with some people!

 

[gozierdt]

Re: How much load on rollers & bunks?

Azlo,

You don't want the strakes to rest right on the rollers. That creates very small contact points (the round roller contacting the rounded strake), that put a lot of pressure on the strakes. I can't see where your strakes are from the pictures, but I'd put the rollers roughly under the stringers, and fairly close to a strake- assuming you've got a set roughly where the stringers are. If you get a chance, shoot a pic of the inside of the boat near the stern so we can see what structure is in there, and the bottom where the strakes are. We could advise you better.

 

[JimS123]

Re: How much load on rollers & bunks?

Do you think your the only one that can see a picture?

Sorry but stupid post!

Of course we can see they are roller bunks and no that will not change anybody's mind about how to setup a trailer.

AS noted above (ezmobee) it was expected to see that link yet again and their is another one too.

Does this change anything? NO!

Just cause it's on the web doesn't make it true and just cause a manufacturer says it doesn't make it true.

How about just offering your opinion (what it is) and kill the stupid attitude dude.

Logic IS a difficult thing to argue with some people!

As Ezmobee said, this topic stirs a lot of knashing of teeth. Many recent posts bashed the use of roller bunks and specifically cited that they do damage to the hull. When I saw some of the original responses, I thought that these guys might not have looked at the pics (or maybe they were edited in later). I'm surprised that someone by now has not come on and said that those bunks are totally inappropriate.

I guessed you missed my point. If my opinion differed from the link I posted, I would not have posted it. So, just to claify for you Craig:

Level all of the keel rollers in a straight line at their lowest position. Lower the bunks as well. Put the boat on the trailer, then level it with jack stands and / or blocks. Raise the bunks till they are in tight contact with the hull. Position them outward as far as practical.. If they can be made to line up just inboard of a strake, that is preferred.

Trailer boats came of age in the 1950's and that's how the dealers and old time experts taught you how to do it back then. It's not only logical, but its worked all these years. A lot of misinformation on the net, especially from sources that aren't logical....LOL.

 

[Azlo]

Re: How much load on rollers & bunks?

Its a 68 holiday starcraft i/o. Aluminum boat. If u look at the stringers they are not that strong (from factory). So I added the cross braces that u see now. It almost seems the strakes would be the strongest. Im guessing to place the rollers between the strakes & the stringers?

 

[gozierdt]

Re: How much load on rollers & bunks?

Azlo,

Yes, I think I'd put them between the strakes and the crossbraces. Also, because of the way your aluminum boat is built- with the tube frames running all the way across the bottom plus the extra framing you did, your keel is supported much better than the average fiberglass boat. I'd go ahead with the placement of the bunks between the strakes and the crossbraces, making sure to get the transom well supported by the back keel roller and the back bunk rollers. Do a check to see where the bunk rollers are sitting relative to your frames. Then bring up the bunks from underneath to sit firmly against the bottom plus maybe 1/8" or so. I think you'll have to do the final adjustment after the boat's all back together and on the trailer. Look at the amount of "squish" on the keel rollers. If they are squished a lot- indented by more than 1/4" or so, I'd raise the bunks a little more. The bunk rollers have a lot more contact area, so they won't be deformed as much as the keel rollers, but load them up until they are lightly deformed then bolt everything down. Make sure none of the rollers are bending the aluminum skin in by sighting along the length of the hull- if they are, back the bunk down a little. I think you'll get a feel for it quickly.

 

[Azlo]

Re: How much load on rollers & bunks?

Thanks Goziedrt, the reason why ask is because the PO had the old bunks on the outside of the strakes.

As you can see he had it almost to the edge vs inbetween the strakes and the stringers.

 

[JimS123]

Re: How much load on rollers & bunks?

Well I have to apologize now. I should have looked closer myself at the original pics. You did such a fantastic paintjob that I thought it was a fiberglass boat. I can't see a rivet anywhere. Now, looking at the inside of the hull it paints a whole different picture.

In aluminum boats they usually refer to the "strakes" as additional riveted keels. Mine has 5. Also, I think what is being called stringers are in fact ribs or frames.

The weight distribution suggestions still hold. As far as positioning the roller bunks, I'd set them so that they bridge the lip on the "strake" and the hull bottom itself. That way the force will be distributed. I'd put them outboard of the strake to give maximum support (like they were), but since your boat doesn't look too wide it probably doesn't matter.

 

[Silver Eagle]

Re: How much load on rollers & bunks?

I think the first thing that I would do is go to some of the local marinea's and look at other peoples trailers. Take some pictures of them on and off the trailer .Then go from there. Not all trailers are the same but you will get the ideas .Or just go some place that sells boat trailers and look around .They don't charge you to look.