Axle placement on homebuild trailer

[ar1g3]

I am building a trailer for my 4m long fiberglass speedboat. It has a 28hp Yamaha for power.

I was wondering where I should place the axle for optimal balance?
I have it now so that the trailer keel extends 1m behind it, putting 3m of the boat in front of the axle. Should I move the axle forward or not?

All I can find on the internet is that you should weigh your boat and go from there, but the boat is being restored so it's hard to determine what weight it will be. I just want the axle roughly in the right spot, so I just need to finetune it a bit.

 

[rob2]

If you don't know, how can anyone else????

It may interest you to know that without a thorough assessment and certification of a home built trailer, it is illegal for use on the road.

Rob

 

[sarabande]

CofG can vary depending on whether the outboard is fixed on the transom or not.

If you post a pic, we might have a guess at where the palance point for the boat is, and that will give you a starting basis for placing the axle.

You can run a trailer without brakes up to 700kg, but even if the setup is less than that, I'd certainly build in brakes.

Boat trailers normally have a load on the tow bar of about 70kg, so that gives you one metric. Are you using an Indespension kit ?

 

[ar1g3]

If you don't know, how can anyone else????

It may interest you to know that without a thorough assessment and certification of a home built trailer, it is illegal for use on the road.

Rob

I know it is illegal as of 2012, but the base for this trailer is actually an old trailer I bought second hand. So it's actually a very extensive restoration if you want, with improvements on the frame. I don't know where the limit is for work on a frame before it's considered 'new'?

CofG can vary depending on whether the outboard is fixed on the transom or not.

If you post a pic, we might have a guess at where the palance point for the boat is, and that will give you a starting basis for placing the axle.

You can run a trailer without brakes up to 700kg, but even if the setup is less than that, I'd certainly build in brakes.

Boat trailers normally have a load on the tow bar of about 70kg, so that gives you one metric. Are you using an Indespension kit ?

The outboard is mounted on the transom.
Here's a pic, but without the outboard on:


As said, the outboard is a 28hp, I would say it's between 30 and 50 kilos in weight. And the boat is 4m long.

The trailer will be without brakes, I'd love to have brakes but then you're into a whole other price class. I have a torsion axle off the old trailer I used for parts, it's kind of a budget build.

 

[Pete7]

Lots of unknowns including what happens when you put 20 gallons of fuel in the boat. Any chance the axle can be attached with u bolts so that it can be adjusted afterwards to find the ideal balance point giving some nose weight but not squashing even a tractor?

Pete

 

[Mister E]

It all depends how much nose weight you want but from what you have said the position you have now would probably be about right.

Remember the further back the axle the easier it is to reverse, so my personal preference is as far back as practicle .

 

[Fr J Hackett]

Can you not wait till you have the boat temporarily fix the axle and then by trial and error adjust it's position finally fixing it.

I built a braked trailer and launcher for an Atlantic 21 RIB that I used to run as a dive boat, the trailer was box section with an A frame and single draw bar at the front, using Indispension hubs mounted on a larger box section axle. A bit of a faff but well worth it to balance everything, you could effectively lift and tip the boat off the launching rollers with one hand and little effort.

 

[lw395]

Best guide might be to find photos of similar set ups.
Bearing in mind your outboard is smaller than many boats this size would have.
But the weight of the fuel can be used to trim.
Most powerboat trailers are adjustable.
70kg might be max hitch weight, 10% of the loaded trailer is usually plenty when it's under 750kg.
Trailers vary a lot in unladen weight at this level, which makes it even harder to guess!

I've just checked my RIB, which is a little 4m Avon. 40hp, 70kg engine, top of transom is pretty much 1m from the hubs.
Trailer itself is heavy-ish, but has 1m of drawbar in front of the bow.
I think the noseweight is probably more like 40kg than 70kg, but it tows fine.

 

[Paddy Layback]

Are you allowed to put a home-made trailer on the road? I thought they all need a plate these days.

 

[lw395]

Are you allowed to put a home-made trailer on the road? I thought they all need a plate these days.

Nothing to stop you re-building an old one.
Probably best not to take it abroad.
Must admit I would be a bit cautious of a heavy trailer with no plate on it, e.g. if there was any doubt that it was within the weight allowed for the car to tow.
I have a little box trailer which was home made sometime before I bought it in the 80s.
Since then, I've changed the wheels, suspension units, floor, sides, hitch and some of the metal work.
Trigger's broom!

 

[JumbleDuck]

I thought they all need a plate these days.

http://www.ebay.co.uk/itm/TRAILER-W...ALL-BLANK-VIN-CHASSIS-PLATES-T1-/201567879575

 

[John the kiwi]

For the size of boat and trailer, i would suggest that you want 25 - 50 kg of weight on the tow-hitch.
Under no circumstances should you have "negative" weight on the tow hitch. Its unpleasant to drive and potentially very dangerous.
If you know the masses and centres of mass you can do the maths to find the answer or you can wait until you can actually put the boat and motor (and fuel tank) on the trailer and find the balance points that way.
Being able to adjust the axle via u- bolts is a great idea and commonly done here with small boat trailers.

 

[Davegriff]

Just measured our old speedboat/trailer rig of similar size to the OPs.

Tow hitch to prow retainer thingy is about 1 metre, and prow to axle is 2.7 metres. Transom of the boat overhangs axle by about 1 metre. Our engine is an old 25hp Johnson 2 stroke, so probably lighter than the Yamaha (definitely lighter if an old Yammy).

You'll find all sorts of "recommended" hitch weights if you search the internet, but I reckon 10-15 percent of weight of trailer + boat etc would be about right. In this case, just keep the balance so its still liftable at the front and easily manoeuverable, and use some trial and error road testing. You can always load the boat (fuel tank, anchor etc) to adjust.... Avoid negative loads at all costs of course!

And don't forget to add a safety chain/strap between trailer and car!

 

[Capt. Clueless]

Just stay away from the new VOSA pull in site on the A14 at the Ixworth/Woolpit junc. Besides the obvious foreign plated HGV's, they're living the dream pulling in trailers for checking. Quite often one or two in there.

 

[William_H]

As said you will need to be able to either move the axle or move the boat fore and aft to get nose weight correct. Your estimation is probably OK for initial set up and as said you will still need to be carefula bout where you put fuel and gear. olewill

 

[VicS]

As said you will need to be able to either move the axle or move the boat fore and aft to get nose weight correct. Your estimation is probably OK for initial set up and as said you will still need to be carefula bout where you put fuel and gear. olewill

best place for fuel and gear, esp anything heavy, is in the car!

 

[Jim@sea]

If you don't know, how can anyone else????

It may interest you to know that without a thorough assessment and certification of a home built trailer, it is illegal for use on the road.

Rob

In the early 1960's many people who bought boats needed a trailer and would buy a caravan for £100 and remove the body. if done today that trailer would be legal,

 

[ar1g3]

Thanks for all the replies people! I will put the rollers etc on and test fit the boat with the outboard on to see if the nose weight is about right. I'm bolting the axle on permanently after the test fit, I think if the weights are about right I can always finetune it by moving the fuel tank around as suggested.

As for the legal/illegal argument, there's no way to prove the trailer is old apart from the several layers of old paint, but there were no VIN plates on the trailer I used as a base. Before 2012 you were allowed to weld something together in your shed, put wheels under it and tow it. At least that's how it was in Belgium. Most boat trailers you find for under 500€ are homebuilt contraptions, and that was my budget. So my way of thought is, if I am going to use a homebuilt thing I might aswell buy an old one and restore it so I know all the welding is done properly, etc.

 

[William_H]

One simple trick to estimate nose weight of the trailer is to stand on the tow ball yourself with no trailer attached. Measure the depression of the rear of the car. Then compare that depression of the car with what you get with the trailer attached. Hopefully something similar for a bigger boat. say 80to 100kg. Experts advise about 10% of total trailer mass. olewill

 

[PowerSlapper]

In the early 1960's many people who bought boats needed a trailer and would buy a caravan for £100 and remove the body. if done today that trailer would be illegal,

There, fixed that for you. It is called the Construction and Use act and changing the construction and/or use could/would render the trailer illegal.
Regrettably what was OK in the 60's or 70's is not acceptable today.
FWIW the DVLA/DOT/Police seem to be having a field day at the moment with mobile vehicle checks. HWMO got stopped a couple of weeks ago. Park on the weighing pads to check axle loads and trailer weight, checked trailer and vehicle plate. Had a chat (very amicable) seems they were looking for over weight HGVs, Tachographs etc, also looking at plant and domestic trailers. According to HWMO once they saw he was pulling a commercially built, plated trailer they were quite relaxed.
For some reason I do not think fixing your own (fake) trailer plate would fool the boys in blue.