College Project

[Guest]

I'm a college student and am doing a design technology project of a lauching trolley/road trailer combined for my Laser dinghy. Currently for this type of dinghy people use a lauching trolley(low to the ground, doesn't rust easily, light) to launch and they pull the trolley onto a road base (suspension, bearings, bigger wheels) for road towing. I was hoping to combine these two tasks with one trolley, but have come accross several problems that I can't answer:
-How much suspension is needed, if any?
-How do I stop bearings from rusting?
-What is the lightest type of suspension?
-What material would be best for the frame?
-What minimum thickness tubing could be used?

Any help with this, or anything else that's important, would be much appreciated.

Regards

LW

 

[Trevor_swfyc]

Why not take a look at a maufacturers trailer to get some ideas. I had a combi trailer years ago for my Fireball made of galvanised steel. Stainless would be better but expensive and not easy to weld (as far as I know). The salt water rusts wheel bearings because if they are quenched in salt water the water is actually sucked into the bearing. As you are building a combi the whole point is not to put the road trailer into the salt water. Are you going to build a gunwale hung launching trailer it must be possible to improve on the design to secure the dinghy at this point to the trailer.
I had to change to a cruiser eventually when wife discovered you didn't have to get soaked to enjoy the water and if it gets windy? you can always start the engine.

Good luck with the project.
Trevor

 

[tcm]

Re: ageing mech eng grad

Hi.

how about rubber cones suspension, as on an old mini? Low tech, rustproof and light? You'll need to do soem rough shockload calcs to show how big, then add a safety margin, then use exactly the same ones as a mini - nice low cost, plentiful spares, no special tooling, nice big ticks.

You can't stop the bearings from rusting - seawater, yes? Note that cars drive about for years on roads caked in salt. Make sure there's room for seawter to escape the roller bearing seats, and access for squirting/greasing the bearings . Price standard low-spec bearings, and the next highest, then dismiss the higher spec bearings on account of cost?

Cost again a big factor for the frame. These things get whacked around - commonest is for galvanised steel I beleieve. Perhaps avoid tube? - seawater will sploosh around and anything that gets in the tube may not easily get out. Use angle or u section - cheaper and easier to fabricate. Also bear in mind how you are gonna export these fabulous contraptions to burgeoning overseas market(!) so if knock-downable an advantage? Same advantgae (perhaps?) for storing the damn thing whilst not in use? whatever.


Good luck.

 

[Twister_Ken]

Hey - do your own thinking! nm

§

 

[mtb]

You have to use over run brakes now car types are not legal.
Indespension are the people to talk to ,they do a very good and quite comprehensive book which has all the legal stuff and even drawings .
free phone 0800720720
you can get them on the net as well.
The only way around the use of trailers adapted frrom cars is to get an earlier trailer and modify it.Hubs can be used ,you will be best getting the book it costs £2.00 or £3.00 posted
Mick


http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v/cheep or swap for tug

 

[tcm]

Re: research and development

nicking ideas from 1 person = thieving, plagiarism
nicking ideas from several people = research

 

[mtb]

Re: research and development

Good stuff just like the germ's and nip's

http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v/cheep or swap for tug

 

[claymore]

You can't do it.
1)You will need to immerse the trolley/trailer for launch and recovery. This will mean that your suspension - forget brakes as it wont be heavy enough to warrant them - will be dunked in (salt?) water. Career suicide and not a marketable product as it will need too much maintenance.
2) There are some smart people out there - if it had been viable, it would have been done by now.
Carrying on regardless - look at the indespension units and go for the lightest they sell. Spraying or painting diesel on the suspension is one way of keeping the rust off - of course it will get everywhere, stinks and won't go down too well with the other beach users .
The laser is a light boat and doesn't really need a trailer SO
Change your project
Design a box trailer that you can put all your gear in (tent, sleeping bag, sailing clothes). It needs to be around 6'X4' (think about plywood sheets). Then think about a demountable rack that would take the boat on the first level and a trailer on a level above.
Use half inch box section but go for inch for the main frame.
Whilst you are making it, once you've done the welding - run molten waxoyle into all your sections then blank off the ends - (it would be good to run your wires down the boxes for your lights) or get it hot dip galvanised. As I said - trailer brakes are a pain so keep it light enough so you don't need them - look up towing legislation - the RYA will be good here. Get a jockey wheel and if you can get away without brakes, build some chocks into your project for parking
Hope this helps.
John S
PS
Use a printoff of the forum thread as evidence of your research and put it into your bibliography - perhaps even stick a screen dump (print scrn SysRq) and use that towards I.T Keyskills if you need to.

 

[tcm]

Re: fight breaks out in staffroom

- bearings are ok with some saltwater - cars get spray all the time.
- don't us box sections - they'll corrode with salt
- if using box sections, don't fillem to prevent rust - tellem to buy a new one.
- don't run the wires down inside of box sections in case u neeed to weld/fix and
also a total pain to assemble.

UNDER NO CIRCUMSTANCES listen to university types (incl my pa) who say "if it was a good idea it wd have been done by now". The clever ones think everyone wd have done it by now, the stupid ones don't realise, and most others do a good job - but they do it BADLY. Note anyway that most people are stupid.

 

[claymore]

Superior knowledge

I bow to it - I will not be dragged into a cyberscrap - If done properly my methods will serve well enough. My own trailer has lasted a good number of years - including a conversion from horse drawn. As you will notice from the many posts I have carefully created, I am a being of considerable intelligence gifted with more than a modicum of kindness. It should be noted that failure to ignore my instructions may well lead to a public flogging, once I have replaced my broken cane with a new one from the Sisters of Mercy retail outlet.

 

[tcm]

Re: helpful hints

http://home.freeuk.com/mkb/catalog.htm

well worth a look for those pursuing a career in education!!!

 

[mtb]

Re: Superior knowledge

Soundslike a reply is required from PB

http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v/cheep or swap for tug

 

[ParaHandy]

If the frame is going to be roadworthy, it's weight might be beyond what a young person can easily handle? (Many tow these things at +70mph) Be careful with the ground clearance. The higher it is, the deeper the water has to be to float it off and the more difficult it will be getting the trailer back on shore whilst the boat is unattended. Clubs don't like their slipways cluttered with big trailers. You could talk to the Laser Centre in Banbury, their Hawk Formula 1 catamarrans are (or were) not road legal (too broad) and a v. complicated structure is required to tilt them & thus reduce width. If not a Hawk, they've other designs which could benefit from a fresh approach.

Good luck.

 

[Avocet]

Yes it's true cars get sprayed wit hsalt water every winter but not immersed in it! This is where it all goes pear shaped. You arrive at the slipway with warm bearings, dunk them in cold water and the air inside the bearing housing contracts. The seals only work to stop the grease getting out (they're only lip seals) so the salt water sucks straight past them and ruins the bearings. It used to be possible to buy "bearing savers" - a spring loaded cap that always kept the housing under a positive pressure (in theory). In practice I don't think they worked that well.
What the hell, wheelbearings are cheap!

Why not design something with very big wheels so that the boat sits low between them and floats off before the axles go under? You could use a couple of space-saver wheels off a sportscar or a motorbike. The tall wheels could then act as docking poles for your boat to fit between.

Re. choice of material, why not go for a composite? If it was cleverly designed in carbon fibre (or even GRP) you could use the trailer chassis as a spring. You don't need brakes if it weighs less than 500kg fully loaded and if you can't make a trailer for a Laser that light you should fail your course anyway! If you go fro metal, beware dissimilar metals in electrical contact!

 

[Avocet]

Yes it's true cars get sprayed with salt water every winter but not immersed in it! This is where it all goes pear shaped. You arrive at the slipway with warm bearings, dunk them in cold water and the air inside the bearing housing contracts. The seals only work to stop the grease getting out (they're only lip seals) so the salt water sucks straight past them and ruins the bearings. It used to be possible to buy "bearing savers" - a spring loaded cap that always kept the housing under a positive pressure (in theory). In practice I don't think they worked that well.
What the hell, wheelbearings are cheap!

Why not design something with very big wheels so that the boat sits low between them and floats off before the axles go under? You could use a couple of space-saver wheels off a sportscar or a motorbike. The tall wheels could then act as docking poles for your boat to fit between when recovering it from murky water.

Re. choice of material, why not go for a composite? If it was cleverly designed in carbon fibre (or even GRP) you could use the trailer chassis as a spring. You don't need brakes if it weighs less than 500kg fully loaded and if you can't make a trailer for a Laser that light you should fail your course anyway! If you go for metal, beware dissimilar metals in electrical contact!


Good luck!

 

[Trevor_swfyc]

Re: College Project (Eureka)

Just had one of those eureka moments, as the laser is not very heavy. How about this idea for overcomming the bearing rust problem. Have launching wheels (smaller) and (larger) road wheels. The road wheels have a roller bearing which is attached to the wheel this fits on a spline on the axle. A quick release system enables the quick removal of the wheel with the bearing. Then slide the launching wheels onto the spline, these can be plastic. The point of using smaller launching wheels is to lower the trailer for ease of launch & recovery.
Obviously this idea requires development what do you think!
Not impressed well what do you expect for free.

Trevor

 

[mikesharp]

I did know someone who used to change his wheels and bearings after arriving at launch site and before going into water. This way he avoided the hot bearing problem and the water using bearings kept their grease in.
Think of a way of doing this mechanically and that problem could be solved, perhaps a lifting axle like they have on some lorries?
On the trolley construction use open sections so you can see whats going on.

 

[vyv_cox]

Re: fight breaks out in staffroom

Salt water spray from the road is completely different from immersion in seawater. Bearings are invariably warm when the trailer arrives at the beach but the boat owner, in a frenzy of enthusiasm to launch, cannot wait for them to cool down. He backs the trailer into the sea, upon which the bearings, and the air within them, cool down. Since they are fitted with lip seals there is no hindrance to fluids entering, so a few millilitres of seawater enter each bearing. That's it, bearing destroyed.

Every commercial boat trailer is made from box section. The strength and modulus of box section exceeds every other form, except round, which is a pain to fabricate. Just make sure they are fully welded and don't allow water in. If this is unavoidable put drain holes in to let it out again.

 

[Guest]

Thanks for the replies - I was thinking about pultruded? carbon fibre rod or tube, but I can't find anyone who sells small quantities so can't get a bearing on the price. If the frame flexed, would I not need suspension?

LW

 

[vyv_cox]

Sprung v unsprung weight

Not having suspension means that the trailer itself is unsprung and takes tremendous shock loadings. Perhaps the classic example of the problems this causes is the Lotus 7 rear axle, a high proportion of the total car weight. As it is a live axle it is unsprung. After a few miles it begins to distort and becomes impossible to seal. Hence they all leak oil.

An unsprung trailer, with maybe a sprung boat on it, could be made to work with very clever design but its material (carbon should be good) and joints (not so sure about them) would need to be able to resist considerable loading. Reducing joint stress, e.g. by triangulation, makes the whole thing more rigid and therefore more prone to break up.

You also have some conflict in its intended use. Putting the wheels right aft, with the boat in the middle, helps your flexing chassis idea but makes it difficult to move about as a trolley. Interesting project. Try http://www.compositespars.com for materials.