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#1 Fra-9816

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Posted 07 November 2012 - 11:01 PM

Hi,

We would like a better rating in IRC (like everyone...) with our prism 28 (0,991) and we think to had more weight in the boat. 1750 kg yet, we think to had 10%.
With the IRC simulation, we will be at 0,980 but the rating will grow slowly after measurement with new shape of the hull in the water.

What do you think about the new speed and performance ?
Where do we put the weight for a better shape of the hull in the water ?
Is it a good deal ?

Usualy Our boat is a killer in the light wind and the down wind but in other weather, it s not easy to save our rating.

Thanks for yur help.

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#2 Haguesail

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Posted 08 November 2012 - 05:53 AM

Hi Fra -

This is covered in some earlier threads, but the summary is that adding 3-4% internal ballast won's penalize you and may help slightly (after your official re-weighing and measurement) or result in little change. First recommendation is to have the boat weighed if you have not already done so. Second is that you may augment this savings if you add fixed items that you plan to actually use, like an additional battery, electronics, or autopilot. Best to discuss the benefits of any further addition of weight with the boat designer.

BTW, you are now obliged to show us your girlfriends tits, Newbie!

#3 jolly

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Posted 12 November 2012 - 10:03 AM

mmmm......your boat will be less of a killer in the light and DW when you add weight that's for sure. You might find that adding the weight gets a better rating but also a much worse performance, and then you aren't competitive in any conditions!!

its not about getting a better rating with more weight or less sail, it's more a constant search to try and find a combination that suits your boat the best.

if you struggle upwind in medium to heavier airs you would be better keeping your light air and DW perfroamnce, but finding a way to improve performance in that zone; more crew weight on the rail?, twisted main with open leech at top? a reef?, a smaller headsail?

as an example, your pics show decent breeze and a massively eased outhaul.........I hope that isn't your medium to heavy air setting. ;)

#4 Jambalaya

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Posted 12 November 2012 - 01:07 PM

as an example, your pics show decent breeze and a massively eased outhaul.........I hope that isn't your medium to heavy air setting. ;)

The pictures don't show that, the main is at full outhaul in the shot with the kite up, it's just the main doesn't go to the end of the boom, fairly normal.

Fra, I agree with jolly's post in that you cannot really tun the boat into an all rounder if it's design favours light air and downwind. If you do add weight you'll just create a boat which is more middle of the pack in more conditions. If you want to add weight it's typically fixed into the bilge area around the keel, I would certainly add much less than 10%, you should run a trial certificate with UNCL.

#5 jcc

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Posted 12 November 2012 - 03:56 PM

I am an IRC measurer and in 2010, I weighed and measured a G&S 30 (ex MORC boat) boat weighed 2728kg and rated 1.000. weighed and measured again with the addition of 145kg of internal ballast on the midship centerline. boat rated 1.003.
Adding weight to a lightish boat will change the fore and aft overhang and transom hight. With the weight, the boats LWL increased by around 0.5m. Longer waterline = faster boat.
They felt that the boat being a little stiffer was worth the slight increase in rating.

The boat sails on Lake Ontario where the average wind speed is in the 8-10kt range.

#6 Fra-9816

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Posted 12 November 2012 - 08:35 PM

I did two test certificat:
First one with 10% of weight more of the boat and the 0,991 become 0,980
Second one with 0,5 m2 less for head sail and 1 m2 less for the main, 0,980 become 0,972

But i haven t change the lwp, x, so, etc.... I can t know this numbers.

4% of weight (70kg) more and 0,5m2 and 1m2 less for genoa and main sail seems great qnd good deal?



#7 jcc

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Posted 13 November 2012 - 12:17 AM

FRA-9816
Adding weight without doing the other measurements does not give you much info. A heavier boat would be slower if nothing else changed, so adding 10% more weight without any other measurments would be expected to reduce your rating.
Adding weight does change the overhang measurements and transom height, so I would suggest that adding the weight will result in a slight increase in rating. I do not know how much credit you get for reducing the main area, but I do know that reducing the genoa results in a reasonable credit. I suggest that you just get your genoa re-measured and it will have shrunk enough to give you at least 0.001 credit.

#8 Rawhide

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Posted 13 November 2012 - 10:35 AM

You get a penalty for internal balast, so I would look at strenghtiening the hull with some heavy steel ribs around the keel, just about all production boats are too soft in the hull letting the keel move. Other than that reducing sail. particulay jib size is much more effective than adding wt.

#9 sailingisforfaggytwats

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Posted 13 November 2012 - 11:16 AM

do you even sail bruh

#10 jolly

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Posted 14 November 2012 - 05:26 AM


as an example, your pics show decent breeze and a massively eased outhaul.........I hope that isn't your medium to heavy air setting. ;)

The pictures don't show that, the main is at full outhaul in the shot with the kite up, it's just the main doesn't go to the end of the boom, fairly normal.

Fra, I agree with jolly's post in that you cannot really tun the boat into an all rounder if it's design favours light air and downwind. If you do add weight you'll just create a boat which is more middle of the pack in more conditions. If you want to add weight it's typically fixed into the bilge area around the keel, I would certainly add much less than 10%, you should run a trial certificate with UNCL.


I looked at the right hand UW pic and thought I saw a massive draft depth, like about 400mm from the boom line. Maybe it's an illusion?

thinking on this some more; the only reason I would add weight to a boat is to try and achieve some more stability if it was too tender. Most people I know in IRC racing take weight out so that they go faster and have more fun!!

#11 Jambalaya

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Posted 14 November 2012 - 09:04 AM

I looked at the right hand UW pic and thought I saw a massive draft depth, like about 400mm from the boom line. Maybe it's an illusion?

Gotcha - yes agreed in that photo outhaul is eased but I think it's pretty light air

#12 Pom

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Posted 14 November 2012 - 09:44 PM

Hi Fra 9816
I raced against you at Cowes week this year on a j97 in what was a petty well mixed irc fleet (97's, A31,Corby 30, x332, j92's and a big heavy swan to name it a few) all pretty similar rating and each having there day depending on the conditions.... We might have even got a bit too close on a few occasions....!

You guys seemed to have pace to burn in any sort of flat water and certainy were quick enough downwind. If I remember rightly the Prisim 28 was one of the early 'planning' offshore keel boats - pretty much designed to go fast downwind but maybe giving away too much grunt to be in it upwind .. Also probably not as refined as today's irc lead mines !.

Have you considered doing some keel mods? Maybe get the weight down where it helps, possibly a different or more forgiving profile? Also the sails might benefit from being slightly reduced / flatter - again to help getting it uphill in more breeze. Final thought - how well do all your systems run? How easy is it to change gear? Do you have your max and min setting dialled in?

I am not saying that I have any of the answers or want to be trying to teach you how to 'suck eggs' but I think you have a cool wee boat and would be interested to see how things pan out.

Pom



#13 the paradox of thrift

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Posted 14 November 2012 - 10:18 PM

We have a much larger boat with similar issues to what you are describing FRA 9816. We are very quick in light airs and downwind, but lack pace and height upwind and reaching.

The lack of ability to carry sail upwind or reaching, having to de-power much earlier, rounding up in the gusts are all symptomatic of a lack of stability which the IRC rule penalises very, very harshly in smaller (<50ft) boats.

We have just started some simple modifications to add weight to the bulb by adding two lead castings. The effect of this will be the same as adding 7 crew to the rail of the boat (43ft).

The rating will go down and in nearly all conditions we will be quicker - so it's a definitie win-win.

There will be a penalty in downwind performance, but this is hugely mitigated by the ability to compete on the breeze, hold lanes, etc.

IRC is a pretty stupid rule in the sense that it can penalise very, very harshly boats that are not radical or extreme, but lie marginally outside a set of measurements. You can have a good day out and sail well, beating all the boats of similar size only to discover you're motherless last in the IRC results. You need to work at measurements and stability to get yourself closer in the box to what the rule likes.

PM me if you want some info on the keel modifications.

#14 dogwatch

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Posted 15 November 2012 - 05:11 AM

Have you considered doing some keel mods?


That's the route IRC optimisation of ex-IOR boats or ex-IMS boats has often taken i.e. rules where, unlike IRC, stability is penalised. I haven't heard much of people installing internal ballast for IRC optimisation, although I guess that's less expensive (as in €€€€).

#15 Fra-9816

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Posted 15 November 2012 - 11:00 AM

if I understand,

it's not too bad to do main sail and genoa with less surface aera.
it's not good to add lead because it will be internal ballast


remove the keel and add heavieris too expensive for us.

to modify the keel is hard and expensive ?

http://www.casimages...15910419815.jpg


I can't hope have a polyvalent boat and work the weakness without cut the good point of the boat ?




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