Why not mount your springs and shackles on pieces of angle iron so that you
can move the axle back and forth till you find the sweet spot. Many trailers
are set up that way.
Jim
"Gary Warner" wrote in message
...

So today we raised the trailer frame under the boat and started
to figure out where the axels should be to get optimum tongue
weight. Here's some of what we found / figured:

We figure the boat will be about 3800 lbs and the trailer about
1400. So that's 5200. Most people and books recommend 7%
to 10% tongue weight, so that's 365 to 520 lbs. The truck
we have is rated for 500 lb tongue weight. So we were shooting
for 400 or 450 lbs.

The boat is 22 feet. The side rails of our trailer come together
at the tongue at about 23.5 feet. And we have 6.5 feet more of
tongue there, deciding where to cut it off.

So we placed some blocks at 5' from the back of the
trailer and we setup the scale at a point that would
give us 3' of tongue. The weight was 680 lbs.

Blocks= 5' Tongue= 3' Weight= 680

Then we did this:

Blocks= 5' Tongue= 4' Weight= 680
Blocks= 6' Tongue= 4' Weight= 600
Blocks= 7' Tongue= 3' Weight= 480

So you can see that the leverage of a longer tongue
gave us almost NO change. But moving out blocks
(axel point) up change things pretty dramatically.


Now our gas tank is right at the back of the boat. For the
above measures the tank was mostly empty (maybe 5 gallons)
so I decided to sit back there to simulate some gas. (Some
might think that's an appropriate use for me.) Anyway, my
170 or so lbs didn't change the tongue weight at all. Maybe
a pound or two, but nothing we could really notice. Hmmmm.

Now that we were zeroing in on our target weight we set our
spare tire plus a 50 lb concrete block up near the tongue
area. That's where the spare will really go and the concrete
was to simulate the jack, bow-stop post, and winch that
will eventually go there.

So with everything in place we got these numbers:
Blocks= 7' Tongue= 3' Weight= 540
Blocks= 7' 2" Tongue= 3' Weight= 480


Now that's what we wanted. 480 is a pretty good number. We have to add
16 lbs to that for the actuator, but can also subtract 3.5' worth of
tongue
that we can cut off. The tongue material is 9.4 lbs/foot so that's 33
less
lbs. Anyway, 33lbs - 16lbs = about 17 lbs. ~ So our 480 number should
end up being more like 465 lbs.

Ok, so I've been all exact here and, of course, things will change. We
don't
have the final bunks on the trailer, the concrete block to represent the
jack and stuff was just a guess, etc. But generally, I think we found
our axel point: 7' 2".

Actually, I'm thinking maybe trying 7'3" tomorrow. I don't want too
little
weight on the tongue, but I'd rather have just a slightly larger margin to
play with in case something is wrong.

Ok, any one that's read this far is obviously bored...