Two pairs of bunk boards or one?

[Augoose]

I've got a 20' open bow and it weighs about 2700 lbs. I'm planning on updating my trailer - repairing some surface rust areas, repacking bearing, etc, and since the carpet is starting to rip off one of the bunks, I'll replace those while I'm at it.

My question - I currently have 2 bunk boards that are at least 8' long, maybe 10' (haven't measured yet). I was considering adding another two for stability and to even out more of the weight distribution.

Are my bunks currently to far in? Should they be further out to make balancing the boat less stressful on the bunks?

Will I be gaining anything with the effort? Is it recommended? Any drawbacks?

I believe this is a keel roller style trailer, and currently the keel does seem to be evenly resting on all of the keel rollers.

Thanks!

 

[mike343]

Re: Two pairs of bunk boards or one?

I'd go for four, two just under the motor mounts and two just outside the planing strakes.

 

[Augoose]

Re: Two pairs of bunk boards or one?

Thanks for the input.

Regarding the 2 by the motor mount, do you mean to short ones directly beneath the engine, or are you suggesting two full length ones but just close in towards the keel where they will be in-line with the engine mounts?
Thanks!

 

[SangerTom]

Re: Two pairs of bunk boards or one?

Just found out today that you want to be narrower than the planing strakes or you can crack the bunks. I had 10" and it should be 8"

 

[Sharp Shooter]

Re: Two pairs of bunk boards or one?

I like them under the stringers yet not on the strakes. 4 is better than 2.

 

[xeddog]

Re: Two pairs of bunk boards or one?

This is the way my 21.5' Beachcraft is set up. It's a little heavier than yours at 3250 lbs, but this setup would still work for you. The two inner bunks are probably at least 10' long and maybe even 12'. The two outer bunks are only 8' or so. I don't think the boat ever touches the rollers for the keel.

Wayne

P.S. Yeah, I know that the leftmost bunk is outta position. I noticed that the last time I brought the boat back in. Crap!

 

[erie_guy]

Re: Two pairs of bunk boards or one?

I am no expert, just an engineer with a different opinion. I would merely adjust the keel rollers to evenly pickup the boat weight. I did this on my boat (a 14' tinney) and it now loads easily and straight every time. Just position the rear roller at or slightly below water level and begin winching.

The bunks are to keep it from falling to the side, once the boat is supported on the keel rollers. Observe the blocking of larger boats - keel supports the weight and the side jacks (i.e. bunks) keep it from falling over.

I would also adjust the bunks down so they only lightly support the sides evenly. Maybe a couple hundred pounds force on each bunk. As you mentioned, it is a keel roller trailer.

Enjoy . . .

erie_guy
Port Clinton, OH

 

[gozierdt]

Re: Two pairs of bunk boards or one?

I have a 20' Sea Ray Seville very similar to yours. It's on the factory trailer (when I got it the underside of the bunks still had "20 S" written on them. It uses 4 bunks, two 10' long ones just inside the longitudinal strake, two 5' shorter ones just outside the strake. Here's a picture from the rear:

I took a look, and the factory did NOT set the rollers up against the boat- the bunk mounts are welded on, so I'm sure of that. In most of our fiberglass boats, the keel is NOT an extremely strong member- there is no direct support right over the keel. The area under the stringers is the strongest part of the boat. I think it's very important with these boats to get adequate support directly under the transom. If you put a lot of weight on a keel roller a couple of inches forward of the transom, you're likely to develop a hook in the hull.

 

[Augoose]

Re: Two pairs of bunk boards or one?

All,
thanks very much for all the advice. I have decided to add two more bunks for more displacement. Now its just a matter of measuring them for length and height.

I've read good arguments on both sides - keel supports the weight, keel doesn't support the weight, so I think for now I'm going to do my best to balance the entire load evenly among the 4 bunks and all the rollers.

Hopefully that is a good idea!

Thanks again all!

 

[Augoose]

Re: Two pairs of bunk boards or one?

What a galactic pain it is to align the bunk boards! In the water, out of the water and back on the trailer to test fit, back in the water, out of the water......

I'm close but still not perfect. Need to move the starboard bunk out and adjust tilt just a little bit more.
That, however, will have to wait until tomorrow - what appeared to be a baby water moccasin swam between my legs while I was adjusting the boat as it sat in the water.

I called it quits after that.