Righting moment question- expertise required

   Please help
I'm currently sailing a 16ft skiff, which a lot of you guys would probably not be that familiar with. 
Class rules specify 3 crew but only 2on trapeze. My current crew consists of myself, skipper, hiking at about 75kg at 6ft6". On traps my sheethand is a big bopper at about 115kg and 6ft 3" with my f'hand around 5ft 10" and 70kg. 

My question is, if I decided to start steering from the wire and swapped my f'hand with a 40kg kid who would now take up the hiking role on the boat, potentially how much righting moment would I be likely to lose?

The goal would be to obviously drop 30kg out of the boat without compromising our righting moment too greatly. 

To work it out accurately I imagine you would need to know the width of the boat which is close enough to 1.8mt. 

The ultimate goal would be to give the 16ft skiff national titles a real shake. Anyone that can give me some solid feedback on this will get a significant thanks in my acceptance speech after taking the crown. Also be welcome for a beer at my place whenever visiting our tops sailing Mecca in Belmont, Australia. 

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flano Send Private Message Find Member's Posts Groupie Joined: 06 Aug 05 Location: Australia Online Status: Offline Posts: 46	Post Options Post Reply Quote flano Report Post Quote Reply Topic: Righting moment question- expertise required Posted: 21 Jun 14 at 4:15pm
	Please help I'm currently sailing a 16ft skiff, which a lot of you guys would probably not be that familiar with. Class rules specify 3 crew but only 2on trapeze. My current crew consists of myself, skipper, hiking at about 75kg at 6ft6". On traps my sheethand is a big bopper at about 115kg and 6ft 3" with my f'hand around 5ft 10" and 70kg. My question is, if I decided to start steering from the wire and swapped my f'hand with a 40kg kid who would now take up the hiking role on the boat, potentially how much righting moment would I be likely to lose? The goal would be to obviously drop 30kg out of the boat without compromising our righting moment too greatly. To work it out accurately I imagine you would need to know the width of the boat which is close enough to 1.8mt. The ultimate goal would be to give the 16ft skiff national titles a real shake. Anyone that can give me some solid feedback on this will get a significant thanks in my acceptance speech after taking the crown. Also be welcome for a beer at my place whenever visiting our tops sailing Mecca in Belmont, Australia.

flano Send Private Message Find Member's Posts Groupie Joined: 06 Aug 05 Location: Australia Online Status: Offline Posts: 46	Post Options Post Reply Quote flano Report Post Quote Reply Posted: 21 Jun 14 at 4:27pm
	Thought I'd add a photo just to give you a bit more to work with

Daniel Holman Send Private Message Find Member's Posts Really should get out more Joined: 17 Nov 08 Online Status: Offline Posts: 997	Post Options Post Reply Quote Daniel Holman Report Post Quote Reply Posted: 21 Jun 14 at 4:35pm
	I get 5094Nm at current config, 4922Nm if you get the kid hiking (assuming a 40kg kid is 1.5m and hikes pretty hard) so 3.5% RM loss which is fairly minimal tbh. Don't know lightship for a 16, lets assume 130kg giving 400kg sailing displ in current trim - you can extremely crudely assume resistance is proportional to displ, so you will lose 8% of displ. I reckon that would help esp in a lighter series, assuming the kid can hike / trim / take abuse / hand out the beers / manage all the fishing tackle :-) Looking fwd to redeeming by beer.

flano Send Private Message Find Member's Posts Groupie Joined: 06 Aug 05 Location: Australia Online Status: Offline Posts: 46	Post Options Post Reply Quote flano Report Post Quote Reply Posted: 21 Jun 14 at 4:40pm
	Daniel, your a legend. Exactly the type of info I was after. Probably should have mentioned that crew work is likely to take a significant hit as well. So any change would need to see a substantial improvement in straight line speed to overcome a slight loss in going round the corners.

flano Send Private Message Find Member's Posts Groupie Joined: 06 Aug 05 Location: Australia Online Status: Offline Posts: 46	Post Options Post Reply Quote flano Report Post Quote Reply Posted: 21 Jun 14 at 4:44pm
	Not sure on overall weight of the boat when it hits the water. Hull weight is about 74kg with all fittings. Mast around 15kg, boom 3 or 4kg + the rest I'd assume we'd be close to 100kgs all up.

Daniel Holman Send Private Message Find Member's Posts Really should get out more Joined: 17 Nov 08 Online Status: Offline Posts: 997	Post Options Post Reply Quote Daniel Holman Report Post Quote Reply Posted: 21 Jun 14 at 4:48pm
	Cool. Well a good I14 is 100kg when it hits the water (measurement scope is ex mast, boom, foils, sails etc) and I assumed there would be a bit more boat with the 16 - built in wings, more surface area etc. All the best with it!

PeterG Send Private Message Find Member's Posts Really should get out more Joined: 12 Jan 08 Location: United Kingdom Online Status: Offline Posts: 822	Post Options Post Reply Quote PeterG Report Post Quote Reply Posted: 21 Jun 14 at 4:49pm
	The answer wouldn't be that hard to work out - though having the kid's height would help (makes less difference hiking that trapezing, but it's still relevant. But all anyone could come up with as a number would be something like the % loss of righting moment. To convert from that to would it improve your chances of winning would depend on a lot of other factors - how windy will the races be not being the least. Are you generally overpowered, or underpowered? My advice would be give it a go, and if you could do it with another boat to sail against so much the better. For what it's worth, making some simple assumptions, I reckon your total crew righting moment is going to be be reduced from something like 406 kgm to 391kgm, while total boat mass goes down by 30kg. So not a large drop. A definite winner in light wind (if the kid is as good a foredeck hand!), might cost a bit in strong winds though? Whatever you do don't sack the sheet hand - he makes up more than 50% of the crew righting moment!
	Peter Ex Cont 707 Ex Laser 189635 DY 59

flano Send Private Message Find Member's Posts Groupie Joined: 06 Aug 05 Location: Australia Online Status: Offline Posts: 46	Post Options Post Reply Quote flano Report Post Quote Reply Posted: 21 Jun 14 at 4:59pm
	Don't worry, I won't be sacking the sheethand, look at the size of him. Not the sort of bloke you want to get offside .

rb_stretch Send Private Message Find Member's Posts Really should get out more Joined: 23 Aug 10 Online Status: Offline Posts: 742	Post Options Post Reply Quote rb_stretch Report Post Quote Reply Posted: 21 Jun 14 at 7:10pm
	I'm amazed you can get down to 75kg at 6'6". I would consider myself a slim 6'6" and come at 97kgs. If I could get near your weight I might even be able to try a moth....10 years of trying suggest this will remain a dream....

Daniel Holman Send Private Message Find Member's Posts Really should get out more Joined: 17 Nov 08 Online Status: Offline Posts: 997	Post Options Post Reply Quote Daniel Holman Report Post Quote Reply Posted: 21 Jun 14 at 7:29pm
	Pretty sure Giles Scott is 6'6" and must be about 97 kg, and looks pretty slender. Edit - he was low 80s at that height in his laser days and was a beanpole! Edited by Daniel Holman - 21 Jun 14 at 7:30pm