How fast do you go?

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douglas_family

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how fast do you expect your boat to go in relation to wind speed. I recently achieved 8-9 knots during sea trials on my new cat in 15 knots of wind with one reef in the main (not realy necessay, but took it easy first time out)

On this showing i would hope to generally achieve 2/3 's wind speed, just wondered how this compares
 
My experience of cats (some years ago and only 14'6" LOA) is that you need to sail them in a particular way to maximise the speed. Firstly, it has to be a beam reach, then as she starts to pick up speed, slowly sheet in to take advantage of the apparent wind drawing ahead. Hold your course, but as you sheet in you will end up travelling PDQ on a beat as the apparent wind ends up at about 30-40deg of the bow.

Hope this makes sense. I used to get mine one hull out on a beam reach with the sails fully sheeted in. Coming about was interesting too, as the actual wind ends up nowhere near where you think it is! We also found it faster to tack down wind than to run dead before the wind.
 
I don't think that can be applied to monohulls as their maximum speed is a function of their waterline length, so there will come a point when the wind speed keeps increasing but the boat speed does little.
 
My Iroquois will go anywhere at 7/8kts

I think this is a sort of mild hull speed because its possible to push through that when the wind (and my bottle) increase.

Lots of race orientated multihulls can exceed the wind speed.

What is the new cat??
 
for mono's i'm still interested in performance relative to wind obviously below hull speed. On my dads offshore 8m we could expect 1/2 wind speed in reasonable condition once wind exceeded 4 knots below this would find it difficult to maintain 1 knot. I'm new to cat sailing so i wondered how performance compared with other cats. Obviously lighter airs require greater skill and i'm no expert! The cat is a derek kelsell 45
 
Kelsall wrote a book called - funily enough - Catamaran Sailing. Lots of the multihull books discuss factors effecting performance.

I think there are too many variables in your question for a simple answer:

Wind effect is not linear - that is if you double the windspeed you get 4 times the wind pressure, triple it 9 times etc, etc.

Big performance difference depending on how you are sailing relative to the wind. So going downwind the apparent wind decreases, going upwind it increases. (this is very marked in cats)

This doesn't include variables related to the boat weight setup etc.

I think the best way is just to sail around looking for things to overtake, try not to make direct eye contact and ensure you are drinking tea / eating lunch as you pass them.

Kelsall 45 sounds lovely - any pictures?
 
Might be able to give a few ideas here as mine is a Kelsall 40 /forums/images/graemlins/smile.gif

You may have seen Derek's formulae for comparing relative sailing and motor performance of multihulls. I have tweaked these slightly to give an approximation of actual speeds achieved:

Power: sq root (horsepower x LWL metres / tonnes displacement)

Sail: 5 x sq root(LWL feet x sail area sq ft / pounds displacement)

I find these pretty close to reality. Note the effect of weight - I know a few 40-45 footers that have been overbuilt or overloaded and couldn't pass a pregnant duck!

From my own experience, here are a few figures boat is 38 ft LWL, 5.5 tonnes loaded for cruising, 2x27hp, 62 sq m sail (+ 10 sq m wing mast):

I plan passages on a 7 knot average

Cruising speed @ 2700 rpm: 8.5 kn. Flat out lightly loaded 10-11 kn

Beam reach in 12-15 kn wind: 11-12 kn

Average speed for tradewind atlantic crossing: 7.75 kn

Highest speed 17 kn - wave assisted.

High speeds in windy conditions are really down to how much bottle you have. If you are prepared to fly a hull you could probably achieve 20 knots. Personally I'm a wimp when it comes to reefing!
 
thats really useful. i'll try crunching the numbers at a later date.

performance under engine was poor on trials but folding props are covered in barnicles so this was no surprise, wouldn't be surprised if she was overloaded as she had a lot of heavy stuff on board when purchased. I've removed a fair bit (especially out of the bows!!), but reluctant to throw out to much till we have been on board for a while and have a better idea of whats useful and whats not. We are in the process of setting up a web blog page however the holding page does have a pic.

http://www.double-helix.org.uk/
/forums/images/graemlins/cool.gif
 
It depends - we're a heavy displacement boat. (44ft - 13T)

In light winds F3 and below I'll settle for half or even 40%
F4-5 she really comes into her own - anything between 7 and 9 kts
F6-9 depends more on seastate and relative wind angle - around 7.5kts
 
We assume we can do half wind speed, from say 4knts boat speed to 8knts boat speed, then it starts to drop off quickly, till double figures become only a distant dream. We'd plan at 6knts, and average 7knts in any sort of wind. Max is 12knts, but that was surfing.
 
Good figures from Snowleaopard.

On my Dazcat 10, which is a fairly sporty cruising cat, I can also passage plan at around 7 knots. To windward in 10 to 12 knots true (16-17 apparent) I can maintain 7.5 to 8 knots in slight to moderate seas. Best speed is usually on a close reach when 9.5 knots is sustainable in 10 to 12 knots of true wind (15 to 17 apparent). In strong beam reaching conditions I have topped 15 knots. I think she could go faster, but that's enough for me. I sail her conservatively, reefing in around 18 knots apparent up wind and and 15 knots true down wind - the reason for switching between true and apparent is that, downwind, I want to know what wind speed I will be facing should I have to turn into wind in a hurry.
 
Some trimaran figures to compare from a Dragonfly 920.

In flat water at the fastest point of sailing for white sails in moderate winds (60 degrees apparent) I can sail at or just above true windspeed from 5 to 15 knots true windspeed. I can get boatspeed faster up to 18 knots (but less than true windspeeds) when the true wind increases to 22 knots. At that point it's not a case of the boat not being able to go any faster, more that I'm cautious and back off. Any higher windspeed and boatspeed slows because of seastate.

When using the asymmetric it's fairly easy to sail faster than true windspeed when keeping the apprent wind at 90 degrees, but the asim goes back into its bag at 15 knots true.
 
Thats amazing performance! we will be sailing with our kids so we will always be sailing well within the boats capabilities. i think i'll plan on 7 knots for passage planning to begin with.
 
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