All over the road above 80kph - towing.

What others have said about ball weight and balance is they key, ensure that you have a well balanced boat trailer combination. You need the weight on the tow ball to be in the range where it has enough weight yet not so much that you are exceeding the tow bar or vehicle limits.

I agree with whom ever said that the axles look like they have to go back due to most weight being in the motors. I don't know with cats but single hull plate boats weight forward is much less and the axles end up with a definite bias to the back of the trailer. Maker sure you have good pressures in your tyres as movement on the tyres due to sidewall movement can also contribute to the sways. With the axles going back the effective drawbar should be longer and also help with stability.

What sort of vessel and what does she weigh Neavsie?

Would the Cats windscreen or the rear of the canopy add enough drag to apply additional force to the front or rear of the trailer to effect the ball weight?. It has enormous drag an I still need the foot down slightly down hills.

Im guessing I used 24-25 l/100k.
Hoping to get a NNN ecu and have it remapped. A little more power from 60 to 80 would be handy on inclines.

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Originally Posted by ozscott

What sort of vessel and what does she weigh Neavsie?

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She is a Marlin Broadbill alloy cat with twin 70s and eats the chop for breakfast, lunch and tea, I really have no idea of its weight. I would love to get it off the trailer to get the trailer weight (a big job I think). I know it is as heavy as hell, I only get 20 knots flat out. I can say they when I feel the trailer pushing me sidways, it feels like 50 tonnes.

Being 1987 and NSW made there are no real indicator i know of to get any ideas.

Hi mate.
I've had a fair bit to do with boats over the years. Couple of points for you.
Your canopy is designed for boat speeds, not car speeds, make sure you put it down when towing, it will last much longer and you won't pull the corners out. Repaired soooo many of them.

Just looking at the picture, I think the axle IS too far forward, but only weighing the set up will tell you, it may be actually only a couple of inches, but that can make all the difference.

If there is insufficient weight forward, then sway can occur and there are many things that can start the sway including the canopy up, or even just airflow around the boat, but if the trailer is set up right, then all those things are negated and sway eliminated.

Sway 99% of the time is caused by the axle being too far forward.

If you don't want to weigh, just move the axle back an inch or so at a time and test it. It probably won't take much.
Good luck.
Kev


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Good point Kev, I also might see if I can fold the canopy back to reduce drag for a start. Fit a cover from the screen to the rear should keep the inside dry and let the air slide over it. Should give me a better economy and that little extra power I am looking for. I just noticed that I have lost a bearing cap, bearings are new, will make sure they are all adjusted ok after the trip and check the tyre pressures.

The good thing about folding the canopy down and using a flat cover is that the canopy will last longer, reduce fading and yep, less drag = more fuel economy.

If the flat cover covers the whole deck opening, drag will be reduced and it has the added benefit of protecting the boat/load from loss and weather.

Don't forget to just try knocking the axle back an inch or so, test and then knock back more until no sway. It will sort it out and you should be able to sit easy on 100 with no issues.

Btw...luv those boats mate, they have a great rep for offshore work....may be a few years old, but they got it right.
Kev

from here

too much rear weight on the trialer (or if the downforce is correct on a jocky wheel then the hitch is too high on the trailer

top heavy load

Too much top drag.

you may also have dying springs on the rear of the trailer thats upsetting the trailers natural balance. The super quick check of that is to up the rear tyre pressure drop the front tyre pressure and see what happens

My 2 cents worth is it looks like the axles are too far forward, moving them backwards will also help with reversing.

I put on some bearing buddies and checked the tyre pressures, they are all the same. Im pretty sure that the drawbar sits horizontal but ill have a have a better look again. The springs have seen better days as well.

I just measured the axles to make sure they are even across the trailer from the hitch, they are good as well. Looks like I need to test the springs or the balance next.