Bunks extending back past frame?

I read on another thread where TD said when replacing bunks he usually runs them around 6" past the back edge of the trailer frame. I believe another individual mentioned a trailer with bunks 18" past/behind the trailer frame.

I have a 16', probably 400 to 500 pound fiberglass boat with a 200lb Merc500 on the back. Right now I have 2ea, 2x6 treated pine bunks placed flat side up. My bunks are extending 8" behind my trailer frame. How far back on that 8" length can I permanently position my boat without fear of breaking the bunk 2x6 board?

I will be able to balance the boat wherever I want as my axle will move where I want it to. I want my boat back on my trailer as far as is reasonable.

I plan on putting a second set of bunks on my trailer (2x4 turned edgewise) after I get the first bunks and my boat in position. I think it would be easier to get this second set of bunks adjusted properly with the boat already in position.

So taking into consideration that my boat sitting on the flat 2x6s is a temporary situation, how far back on the 8" of bunk extension behind my boat would it be safe to rest my boat?

I realize this is quite possibly a difficult question to answer but I was hoping someone might have a gut feeling on this.

Re: Bunks extending back past frame?

I'm just bumping this thread because I'm interested in the reasons for extending the bunks beyond the frame if the balance can be achieved without the extension.

Re: Bunks extending back past frame?

Most people do this to ensure that their transom is always on the bunks rather than the possibility of not getting the boat on the trailer far enough and the bunks possibly damaging the hull ahead of the transom. These extensions are not normally used to allow you to load the boat farther back on the trailer. Although you could move them back a bit you don't want an excessive amount of weight hanging off the back of the bunks unsupported. If you were to have the boat unbalanced it's possible it could break the bunk boards if they were overloaded.

When you extend a timber past the final support that support becomes a stress point. When weight is applied to the timber it presses down on it causing stress back up at the mount. If too much weight is applied it would snap the timber at the mount.

18"-24" extensions on the bunks should be just fine but you want to ensure that you aren't using them to load the boat back too far creating stress on your bunks/hull. Bunks are there to distribute the weight of your boat. *EDIT* IMO you should never have the transom resting at the end of a 18-24" extension!

Perhaps extending the tongue to make your trailer longer would be a better approach.

Re: Bunks extending back past frame?

burroak said:

I'm just bumping this thread because I'm interested in the reasons for extending the bunks beyond the frame if the balance can be achieved without the extension.

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Because the trailer I'm switching to is about 8" shorter than my old trailer. I don't want the boat closer to my towing vehicle if I can easily avoid it. I could make it work with the boat 8" closer but if there is no problem with moving the boat back on the trailer, I'd rather do it that way.

Re: Bunks extending back past frame?

burroak said:

I'm just bumping this thread because I'm interested in the reasons for extending the bunks beyond the frame if the balance can be achieved without the extension.

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I think what he was aiming to do was put his boat as far back on the trailer as possible. (Low water loading maybe?) If he can move his axle he's keeping the tongue weight balanced but trying to lengthen the trailer by extending the bunks.

Re: Bunks extending back past frame?

PondTunes said:

Perhaps extending the tongue to make your trailer longer would be a better approach.

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I am considering this option. The bunk extension would be an easier option. And I may not have to do either but I'm wanting all the information I can get before I decide.

Thanks for the reply.

Re: Bunks extending back past frame?

you misquoted me. i have ran 2x6 bunks, on edge, not flat, as far as 24 inches past the trailer frame. i said i always run my bunks 6 inches past the transom of the boat.

Re: Bunks extending back past frame?

tashasdaddy said:

you misquoted me. i have ran 2x6 bunks, on edge, not flat, as far as 24 inches past the trailer frame. i said i always run my bunks 6 inches past the transom of the boat.

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Sorry about the misquote. I remembered you saying something about a 6" overhang. And I believe it was so you could get the tongue weight right.

But anyway it appears, correct me if I'm wrong , that you are familiar with letting transoms hang out past the rear frame of a trailer as long as the transom is well supported by adequate bunks. That is the point I was searching for.

TD, are you familiar with rigs that have the boat transom well supported on trailers with the transom at least 8" behind the trailers frame?

If so the only inconvenience would appear to be fitting a transom saver to hold my motor up. I think I can solve this inconvenience.

Re: Bunks extending back past frame?

yes most of my boats, hang farther than 8 inches past the frame, and the tramson saver is a PITA. as i have said in the past i like long tongue trailers, i repostion my axle so i can move the boats back, and use 2x6 on edge for stringers, on the heavier boats. the aluminum, i use 2x4. 2x6 or 2x4, is really defined by what is hanging on the transom. i do it this way 50 hp and under 2x4.

Re: Bunks extending back past frame?

Obviously on edge bunks can support more then flat bunks. You don't have enough boat weight to be concerend about it.
My bunks are about 24" past the frame, however my transom is only about 18" past the frame.
You will be better off extending the tongue, moving the boat for balance, and correct tongue weight.

Re: Bunks extending back past frame?

I set up my boat trailers so that bunks are a about 1" past the hull. Any more can cause unloading problems. I also pay attention to the last support, for the bunk. I do not like to span more that 6-12" past the last support. That depends on whether you are using 2 X 4's or 2 X 6's.

Re: Bunks extending back past frame?

i keep hearing people say longer bunks cause loading and unloading problems. that's just the reason i extend mine, and move the axle. it makes loading all my boats easier. longer tohgue, you get deeper into the water, when loading they help center the boat, when properly installed