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Effect of weight on boat speed

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Post Options Post Options   Quote stonefish Quote  Post ReplyReply Direct Link To This Post Topic: Effect of weight on boat speed
    Posted: 22 May 19 at 7:56am
Does anyone know how boat weight effects speed on a planing dinghy for example a Comet, Solo, Streaker etc?

For example how much faster would a boat that weighs 95kg go compared to a boat weighing 100kg if all other variables like helm weight etc are the same between the boats?
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Post Options Post Options   Quote andymck Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 8:35am
There are many more variables than just boat weight.
A lighter helm boat combination will plane earlier and accelerate faster.
Depending on where the weight is in the boat, there can be other affects. We all talk about trying to keep the weight out of the ends of the boat to reduce pitching moments.
The bottom line is 5kg will not make as big a difference as skill level for most of us. But an equal skilled sailor in a lighter newer boat will be quicker, all other variables being equal.

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Post Options Post Options   Quote davidyacht Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 8:51am
Newtons Laws apply and as Uffa Fox said “the only use for weight is in a steam roller”.  That being said, any difference will be most apparent when “like for like” racing, and will manifest itself as a lack of acceleration compared with similar but lighter boats, and possibly lateness to get on the plane.  Obviously it is the all up weight that also counts ... so the combined weight of helm and boat has to be taken into account.  If I were looking to buy a boat, I would avoid one that is overweight.
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Post Options Post Options   Quote ifoxwell Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 8:53am
I agree. In most conditions, all other things being equal, the effect would be negligible... but on a marginal planning day the ability to push past your bow wave earlier could make a big difference in a one design fleet
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 9:11am
A 5% difference in hull weight won't make 5% difference in speed over the wind range, in fact I'd suggest it would be completely unnoticeable in most conditions. But if I was buying a new boat I would expect it to be bang on minimum weight. A used boat OTOH there are so many other factors that 5kg would not put me off buying an otherwise good boat.
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Post Options Post Options   Quote H2 Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 10:24am
Focus so far has been on acceleration but you also need to factor in how a boat responds in the lulls. Many of the older designs which are heavier also are able to maintain some momentum in lulls which means they can ghost across the calm patch and get into the new breeze and they also remain able to steer longer. The lighter boats on our pond accelerate faster but also slow down faster!! Hope that makes sense?
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Post Options Post Options   Quote H2 Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 10:25am
Related to this is how heavier boats deal with waves on a light wind day. Try catching a K1 upwind on the sea in a light breeze if you need convincing! 
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 1:50pm
And usually heavier classes of boat (older boats) have a more displacement biased hull form which means they carry way better in the lulls anyway.
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Post Options Post Options   Quote tink Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 6:20pm
I know the post is about boat with but bare with me, I bought a Streaker because with its ideal weight is 73kg (based on class recommendations and ties in with the average to ten helms weight for a number of years at the nationals) so I would keep my weight down and healthy. My boat is 20 years old, all wood, been repaired a few times and I suspect heavily overweight. For most of my time I was at the top end of the weight range but after a few years of getting to know the boat frequently I would be at the windward mark with the lighter, more experienced helms in much new boats and better rags. When we went down wind however despite being right alongside hot shots and in clean air they would get on the plane and just get away from me. I would copy exactly what they where doing but still couldn’t get it on the plane as quickly as they did and it made a big difference. 

I have recently moved clubs and can keep up most of the time with much newer all plastic boats especially when it is blowing. I am still learning wind patterns etc of the new club but feel I doing OK 

So I would say upwind probably no difference it as all about technique 
Off wind it makes a difference especially in conditions when others can get on the plane and you can’t

I am doing nationals in a few weeks and I am unable to replace my boat at the moment I have been on a weight lost plan 12kg since January and the hull and foils are being polished within an inch of there lives. Hopefully the boats weight will only have a small percentage of detrimental performance as some above are suggesting.
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Post Options Post Options   Quote tink Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 19 at 8:08pm
Lots to read here


But graph on page 59 though crew weight shows how insignificant effect though the preamble says ‘The effect of crew weight is studied by comparing time deltas for crews of different physique relative to a baseline 80kg sailor. Results show relatively high sensitivity of the performance around a race course to the weight of the crew, with a 10kg change contributing to time deltas of more than 60 seconds relative to the baseline sailor over a race of one hour duration at the extremes of the wind speed range examined.’

This therefore by extrapolation hull weight is, however I think this must only be displacement mode




Edited by tink - 22 May 19 at 8:20pm
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