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Author Topic:   Trailering: Calculations -- I disagree (a bit)
triblet posted 03-28-2002 11:44 PM ET (US)   Profile for triblet   Send Email to triblet  
First: I think there's some really good stuff
in the article. I've adjusted my tongue
weight twice using what I believe to be the
same calculations. Both times it ended up
right where I expected it it. I moved it
a second time because I decided I wanted
even less tongue weight.

BUT: I STRONGLY disagree with: "Moving the
boat is easier, but you may not want to move
the transom away from the end of the
trailer." Both times I did it by moving the
axle. The first time it took an hour, the
second time about 45 minutes. Moving the boat A) would have taken a lot longer, and
B) would have ended up with the transom off
the end of the bunks, which is really bad

All I did was lower the trailer jack all the
way, put a couple of jack stands under the
back of the trailer, raise the trailer jack
all the way (now the tires are off the
ground), loosen the four U bolt nuts on each
side, bang the axle forward with a small
sledge (be careful where you bang), tighten
nuts, lower jack, remove jack stands, raise
jack to normal position.


Jerry Townsend posted 03-29-2002 10:39 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Chuck - point understood - and certainly in your case where your axle is apparently unsprung - moving the axle would be quite easy. However, should one have a trailer with one or more sprung axles where the spring mounts are bolted to the frame - moving the boat (via moving the winch stand and boat) is a perhaps a bit easier. But, it makes little difference which way is taken - both roads lead to Rome - though one might be a tad longer. Appreciate your comment. ----- Jerry/Idaho
triblet posted 03-29-2002 11:09 AM ET (US)     Profile for triblet  Send Email to triblet     
I have a sprung axle. It was still easy.


JohnAz posted 03-29-2002 12:18 PM ET (US)     Profile for JohnAz  Send Email to JohnAz     
JBCornwell posted 03-29-2002 12:53 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
I don't know what article I missed, but I agree with Triblet.

The boat is moved only to get the support in the correct locations. Most important is support directly under the transom and/or keel.

The carriage that fits the springs and axle(s) to the frame is moved to adjust balance of the whole rig to get 7% to 10% of the towed weight on the hitch for a single axle trailer, 5% to 7% for a tandem.

Some carriages are bolted to the frame; move them anyway. If you need new bolt holes drill them or, even better, use "U" bolts to secure it.

The easier arrangement holds the carriage to the frame with 4 or more "U" bolts. Then you merely loosen the "U" bolts and slide the carriage to the new position.

If your spring shackles are bolted to the frame, rather than to a movable carriage you either have a trailer custom built for that boat, and no other, or you have a trailer too cheap to carry a Whaler.

The above comes second hand from an engineer who used to work for Shoreline. He saved me a lot of grief.

Red sky at night. . .
JB :)

jimh posted 03-29-2002 03:21 PM ET (US)     Profile for jimh  Send Email to jimh     
The article to which Chuck alludes is .

The topic of how to properly rig a trailer and position the boat with respect to the trailer frame is covered at length in

Jerry Townsend's article is really more about pre-calculation of tongue weight changes that result from boat position movement than an exhaustive treatise on trailer rigging.

jimh posted 04-01-2002 08:32 AM ET (US)     Profile for jimh  Send Email to jimh     
Jerry Townsend has created a DOS executable program to aid in performing all the calculations he described. A link to the program is now included in the article.

As for the one sentence of the article that Chuck objected to, I have added a hyperlink to my article on trailer rigging that explains the pro's and con's of moving the boat. I also added a hyperlink in that article back to the article on calculating the tongue weight.

In the rigging article the notion of not moving the boat nilly-willy on the trailer to adjust the tongue weight is (I thought) well described and the benefits from rigging it that way are presented.

If a boat is on a bunk trailer, I don't think that moving the boat farther forward is really a problem. You'll just be moving more onto the bunks. In the case of keel roller trailers,
you clearly want to leave the boat in a position where the transom weight is supported on a keeel roller.

Actually, on my trailer, the bunks extend well past the transom. At one time the boat was rigged with the transom about a foot farther aft. As I recommend in my article, I moved the boat to where I wanted it to rest on the trailer, rigged the trailer rollers and bunks, then moved the axle to get the tongue weight. When I finished I had a foot of bunk sticking out the back.

triblet posted 04-01-2002 11:02 AM ET (US)     Profile for triblet  Send Email to triblet     
I also have a bunk trailer. Again, moving the
boat would have been a lot more work. Since I
was reducing the tongue weight, moving the boat
aft was not an option. And had I been trying
to increase the tongue weight, moving the boat
would have moved my truck closer to salt water
when launching.

Maybe it's different if you launch in fresh


Jerry Townsend posted 04-01-2002 03:18 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Chuck - the choice of moving the boat or the axle(s) is that of the owner of the outfit and in the case of your boat - the decision is yours! But, you have two choices - either the boat or the axles - either (or both) will do the job. The write-up simply presents the necessary formulations for those interested to get an idea of what is going to be required. That is, if a hitch load is too light or heavy, the owner can get an idea on how much the boat and/or the axles need to be moved.

The trailer load balance write-up addresses each option and does not make a recommendation, per se, regarding moving the boat or axles - as that decision rests solely with the owner of the outfit.

Also, trailer load balance adjustments normally require the boat or axles be moved but a few inches - not feet. The reason for this is that the boat weight is principally carried by the trailer wheels and the C/G of the boat being but a few inches in front of the axle.

Jim has provided a very good write-up in the REFERENCE section regarding many aspects concerning a trailer. Those words are appropriate and germane. ----- Jerry/Idaho

triblet posted 04-01-2002 10:28 PM ET (US)     Profile for triblet  Send Email to triblet     
I agree that it's the choice of the owner,
but it DOES make a recommendation:
The page says "Moving the boat is
easier". Not only is this is wrong (which
makes more work for the owner), but
moving the boat is potentially damaging to
the boat.

I checked out the trailers in the launch
ramp lot this weekend. On most it would be
easier to move the axle than the boat. Jack,
loosen, move, tighten. A one-beer job at

Moving the boat requires moving that which
supports the boat (rollers or bunks) so that
the transom is still well supported. The
transom is both the strongest and the most
heavily loaded part of the boat (because your
Yama-rude-zuki is sitting on it). It must be
solidly supported. If you move the boat it
won't be solidly supported unless you also
move the supports. Move the boat aft and it
isn't supported at all. That's real bad.
Move it forward, and it isn't supported as
well as it could be if there were a roller
or bunk bracket right under it. This means
that the other rollers or bunk brackets are
punching your whaler in the belly on every
bump. And if you move it forward, your truck
is closer to the salt water. Every inch
counts. I traded my '95 Pathfinder last year
after launching in saltwater most every
weekend day for three and a half years. Not
a single spot of rust, because it never got


Jerry Townsend posted 04-04-2002 11:33 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Chuck - I finally got back to the FORUM - and indeed I make the statement that 'moving the boat is easier ...'. The word 'is' is wrong and should be 'might be' or 'could be' or something else. I wouldn't even think of opening a discussion regarding ' depends on what the word is - is ...'.

But seriously, hopefully I have not made any more errors in the poor choice of words - but, if I have, consider that word in the context of the remaining text. ----- Jerry/Idaho

lhg posted 04-05-2002 02:11 PM ET (US)     Profile for lhg    
I agree, adjust the trailer wheels.

Here's an even easier way to do it, and the method I use on my dual axle 25 Outrage trailer, with 4 wheel disc brakes. Having previously marked the frame for distance to move the wheel carriage, get the boat off the trailer, leaving trailer attached to the car (so the frame remains fixed in position), loosen the four U-bolts clamping the carriage frame to the trailer frame, roll the wheel assembly forward or backward as necessary, working side to side an inch at a time, retighten U-bolts. No jacking is necessary, as the wheel carriage will slide easily relative to the frame. It's a 1/2 can of beer job!

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