Home Made Raft

captain359

Hello Everyone,
I thinking of making a raft for a local upcoming raft race, It has to hold 4 guys and any ideas would be great, I have an idea to use empty 50 litre beer kegs (which i have to return after use !! ). How many kegs would I need to use to float four guys and a sheet of ply ??
Any feedback would be great to assist me in my calculations

Thanks in Advance !!!!!

ART6

captain359 wrote: »

Hello Everyone,
I thinking of making a raft for a local upcoming raft race, It has to hold 4 guys and any ideas would be great, I have an idea to use empty 50 litre beer kegs (which i have to return after use !! ). How many kegs would I need to use to float four guys and a sheet of ply ??
Any feedback would be great to assist me in my calculations

Thanks in Advance !!!!!

Depends on the weight of the guys and the kegs etc, but bear in mind that an object will displace its own weight of water, and that water weighs 1,000 kg per cubic metre. Therefore, if you have a total weight of (say) 400 kg then that will displace 400/1000 cubic metres of water (0.4 cubic metres or 400 litres). So you would need 400/50 kegs, or 8 kegs.

It's many a year since I had to think about such things, but as far as I recall that will simply mean that the platform of your raft will be at the water level surface. To be a bit clear of the surface you would need more kegs -- guess another four or so? Then 12 kegs would have a total volume of 600 litres but the weight would only displace 400 litres of water, so as a rough calculation the kegs would be 400/600 below the surface or 66% below-- a third of their diameters would be above the surface. Then if the diameter of a keg was (say) 400 mm then the platform would be roughly 400 x 0.33 = 132 mm above.

Oh, and you will also need lifejackets and a subscription to the lifeboat service.;)


Personally I would go for full beer kegs and forget about the raft race:D

captain359

Cheers Art,
You input will be of great help, the main reason for using Kegs is that the raft is being built on behalf of a local publican for an upcoming race, the rules state that 16ft by 4ft is max demensions and oars must be homemade the guys doing the "sailing" will be the lightest four guys we can find. The plan is to use a sheet of ply with the kegs underneath and foam filling the gaps underneath and possibly a fin keel for a bit of extra stability. Its going to be a charity event with all the safety measures in place and should be good fun, so you reckon between 8 to 12 kegs should suffice ???

ART6

I don't know if 12 kegs would be enough as I don't know how much a keg weighs or what it's dimensions are. I was just using a figure to illustrate how to work it out.

Basically you need to find out what the weight of a keg is, then add to that the weight of everything that will be fixed to them including people. That is the weight of water that will be displaced when you lauch the raft, and every litre (or one-thousanth of a cubic metre) of that water will weigh 1 kg. To make sure the raft floats above the surface you then need to make sure that the total volume of the kegs is greater than the volume of water displaced. The more it is the higher the platform will be above the surface. That's why iron ships swim:D

Bear in mind that the calculation assumes the all-up weight at the time of launching, so tell your crew no big fry-ups on the morning of the event and no drinking the kegs dry the night before:p

cruizer101

Bit off topic but can I ask where the raft race is on, we used to have one locally when I was a kid but now I'm old enough to be entering its not on anymore, would love to enter one.

Wexford-Bass

Would it be Kilmore Quay... great craic at that last year.