Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

[The_Other_Dave]

I have a '99 Trail Rite trailer that carries my '99 Monterey 180M.

The bunks are in need of repair due to age and some de-lamination
of the existing 2x6" bunk boards.

I can't easily get southern yellow pine here in Colorado (I have checked and checked) and I am not interested in dealing with treated lumber so my choice is really Douglas Fir pine.
So I am interested in putting in some additional strength in the beams.


The sections of the existing bunks between the vertical brackets are bending more than I would like. This
is probably partially due to the age and weakening of the original bunks but since this is a single
bunk per side trailer it seems like it could also benefit from more strength.

The old boards are painted so I cant really check for what they are....but they are pine of some sort and they have some small knots in
them. I definitely wouldn't call them clear pine.....i.e. not really that strong.

I would offset them towards the outside of the hull so the distance between the bunk and the adjacent chine would not change.

I also have 12' wide bunk carpet waiting so that isn't a problem.

The only thing I can think of is increased friction but that might not change as the load on each sq inch of bunk should lower thus decreasing its contribution to friction.....I am also planning on lubing the new bunks anyway.

So is there any reason why I shouldn't widen the bunk boards to 2x8" Doug Fir? Please check out the photos and comment.



Thanks,

Dave

 

[Mi duckdown]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

I would stay with 2x6 doug fir. By the way, how do you keep that hull so clean?

 

[The_Other_Dave]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

Hull is just that nice.....yet another reason I bought it last fall.

It has been polished stem to stern and then waxed by me 2 times since I have owned it......8 months and only 6 trips on the water.

We also boat on water from less than 50ish miles from the snow that melted into it so it stays clean.

I was watching some wakeboarding vids the other day and had to keep reminding myself that others boat in water that I poop in and then ship downstream (treated of course)

Any reasons why you would stay with 6" boards.

Thanks,

Dave

 

[LippCJ7]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

it will not change anything so if you feel the need to go ahead, like you said so long as you take the added width into consideration it will be fine.

 

[dingbat]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

Yellow pine has a strength of 13,100 PSI compared to Douglas firs' 11,900 PSI. Unless your boat weighs a couple hundred thousand pounds, it is not an issue.

 

[Thalasso]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

My guess the sag as you put it is from the shape of the hull. The wood has formed itself to that shape. Does the boards sorta straighten out when the load is off of it? You want them to form to the shape of the hull or you would have to much pressure in one spot.

 

[The_Other_Dave]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

My guess the sag as you put it is from the shape of the hull. The wood has formed itself to that shape. Does the boards sorta straighten out when the load is off of it? You want them to form to the shape of the hull or you would have to much pressure in one spot.

They sag all the time even with the boat off.

There is a gap (small) between the center of the sagging sections and the hull.

You can tell that the 3 points with brackets underneath are holding most of the load of the boat.....so not good.

 

[colbyt]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

Adding to the width will not add much to the strength.

What you can to to greatly increase the strength is add a section of 2x4 vertically between the bunk support and well secured to the bunk board to form a capital T design. I am not an engineer so I can't really tell you load increase values but I know it is a lot. If you do this use well countersunk deck screws or SS ones. A small lag bolt or two through the bunk supports on the end s and it will be extremely sturdy.

 

[The_Other_Dave]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

Adding to the width will not add much to the strength.

What you can to to greatly increase the strength is add a section of 2x4 vertically between the bunk support and well secured to the bunk board to form a capital T design. I am not an engineer so I can't really tell you load increase values but I know it is a lot. If you do this use well countersunk deck screws or SS ones. A small lag bolt or two through the bunk supports on the end s and it will be extremely sturdy.

I think that adding a T 2x4 would increase the stiffness too much. It would eliminate any flex at all.

 

[LippCJ7]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

in all honesty Dave I wouldn't mess with it, it looks like it is supported properly to me from the pics you have posted, the bow in the wood certainly looks to be within proper specs, if the wood was rotting and pulling the screws I would replace them but from the pics I think it looks great, the other thing you mention is that the bunks bow even after the boat is in the water and that too I consider to be normal, all things considered it looks like the trailer fits the boat nicely.

 

[The_Other_Dave]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

in all honesty Dave I wouldn't mess with it, it looks like it is supported properly to me from the pics you have posted, the bow in the wood certainly looks to be within proper specs, if the wood was rotting and pulling the screws I would replace them but from the pics I think it looks great, the other thing you mention is that the bunks bow even after the boat is in the water and that too I consider to be normal, all things considered it looks like the trailer fits the boat nicely.

Oh the bunks have to be changed....the one on the starboard side has a lengthwise crack developing
that is heading straight for the carriage bolt installed mid span.

Just trying to consider any optimization while I am doing it.

 

[LippCJ7]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

Oh the bunks have to be changed....the one on the starboard side has a lengthwise crack developing
that is heading straight for the carriage bolt installed mid span.

Just trying to consider any optimization while I am doing it.

OH well then yes I would replace it too!

 

[dough41]

Re: Any reason not to widen bunks from 6" to 8" (pics to evaluate inside)

Not really too relevant to the question, but I have a 1998 180m I thought I kept nice but the bottom of your boat is like new! Very impressed...