Weight Distribution? - Triple Crown

[Graham_Snook]

Thanks to Kbits and Sailsetc my Triple Crown is coming along in leaps and bounds..

I'm now fitting her out and this is where the problem lies. In the sketch part of the MYA full plans, the winch and steering servo are next to each other quite far aft of the keel box (150-200mm). I went for the Hi tec 5745 (digi sail arm) and it seems to be quite a large lump to have that far back. So with a bit of jiggling I can either:

a)fit it just forward of the mast/keel box
b)fit it just aft of the keel box
or
c)fit it 150 mm aft of the keel box as the sketch suggests

With the beam of the TC I can fit it down the centre line in either of these positions, but it's just knowing which one. I know on full size sailing boats, getting hte weight closer to the keel and the lower down the better..but most full size yachts also have a chunk of iron called an engine! (which is where the sail arm would be)

But then I got thinking...always dangerous!...with over 2kg of lead on the end of carbon fin hanging over a foot below the hull...would 150 grammes aft really make that much difference?

Thanx in advance

G

[Chairman]

If you want to race, do you want to seriously test yourself in competitive racing? If so, bite the bullet and float the hull on her lines. If not, no, 6 oz unbalanced fore-aft doesn't matter that, erm, much...!

[awallin]

I found it interesting that in Arcos some (narrow) boats had maximum weight(75g) rudders. Supposedly this increases the moment of interia for the pitch axis and thus reduces pitching. Should be especially good in conditions where there is big waves and little wind.

So, the ideal weight distribution might not be to have everything around the finbox area after all...

To get the boat floating on its lines I would put the winch where it is most convenient and then adjust the bulb slightly fore or aft to get the waterline right.

[Graham_Snook]

My bath isn't deep enough, and the girlfriend wasn't in favour of me scaring her fish! I told her Epoxy and lead were safe for fish but she didn't believe me!!

I was going to test float without the fin to check the port/starboard alignment, but until I get her (the boat, not the girlfriend) into deep water I won't know for sure about fore/aft trim.

I would like to race, but I'd love to win it's my first boat/season I realise that I'll have to spend more time/money to get better, but I've invested in the winch and the rig in the view of getting a better boat one day, after I have gained more of an idea about RC sailing (which was one of my reasons for building one). It's the thought about weight distribution that makes me glad I have built my own, so I'll know what goes where and why

It's just at the moment I don't know what goes where or why!!

[Chairman]

I found it interesting that in Arcos some (narrow) boats had maximum weight(75g) rudders.

Hi Anders

I'm not convinced about the pitching moment, though it sounds plausible. What I think more likely is that, if the rudder is carbon with a carbon stock, then there is about 55 gm you can put, as lead, right down at the rudder tip. Make it a high aspect ratio rudder, and I think you have a useful increase in righting moment...

[Muzza]

Graham

Consider approaching your local swimming pool manager. Ask to be allowed to bring the boat along very early one morning - I'd suggest before they open. The only people there will be those training - they'll be lane swimming and totally disinterested in the twat with the model boat.

You can climb into the nice heated water, complete with model, and test float her with various components in various places until you are happy. You can eyeball the waterline from waterline level.

To get the bulb in the right place on the fin, consider making a "simple mock up" fin out of sheet aluminium, to the same profile as your proper fin. You can adjust the weight of the aluminium fin to equal that of your proper fin by cutting holes in line with the fin's vertical CoG - it doesn't matter 'cause she won't be sailing with this fin. Pad the top with timber so it fits nicely in the fin box. Use two straps of velcro through two slots in your mock up fin, to cradle your bulb. You can move it fore and aft until you are happy, and then mark the positions carefully before commiting to placement on your "proper" fin.

Sounds like a bit of a palava - but very cheap and very accurate.

[Muzza]

...ps

In Auckland this week it has been very warm - we can just jump in the neighbour's outdoor pool.

I appreciate it's a little cooler in London right now.

Good luck.

[Graham_Snook]

In the end I opted for the position of the arm winch just aft of the keel, and shaped the bulkheads to the the arm wasn't obstructed, then I place the RC gear behind the winch, then the steering servo, all along the centre line.

After burning the midnight oil for two nights she was ready for her first sail, even tho it was half way through the morning sail by the time I got to Clapham. (Via the art shop to buy some rubbers for the bumper) The guys up there helped me to set her up and I was away.

Conditions were light aqnd she was floating bow high, but I feel this was more to do with the angle of dangle of the fin than the weight of the RC stuff

Joined in the first race, and on the start run I was late, and managed to hit the start cone, bow went one side, counter weight the other. Drifted slowly off by which time the rest of the boats were half way up the beat, all together in their own wind shadow, while there was breeze in the centre, I went off in the other direction and before I knew it I was first boat round the mark! - Beginners luck - so it was off onto a reach and away she went, got to the bottom mark and into the wind and there was only one boat close, headed off to the middle of the course again got another lucky favorable wind shift and managed to hold the lead to the winward mark before gybing and heading back towards the line...the next closest boat covered me on the way down, but I managed to stay in front and won my first race!

Then the batteries went flat!:(

A combination of not charging them enough and testing the arm quite a bit while I was building, too much friction in the system - I needed another turning block, so had to run the sheet round the front of the mast and I think the arm was catching on some goo from fitting the deck the night before!

Because of the rush to get her finished for the Sunday racing I didn't get a chance to weigh her, so after the the battery trouble I got my chance and the weight? 250g/8oz under...I think that might explain my luck!

So it's back to tweeking in the kitchen and experimenting with plastascene!

[IanHB]

Graham, you should be both pleased and proud of your fine performance
to build and sail an IOM which can do so well "out of the box". You will now begin the process where, after every outing, you will return to the work bench to change something that will improve the boat little by little as you see other ideas, or think of a better way of doing some task or adjustment.
Then after maybe 12 months you will be keen to do it all again, design and build a boat incorporating all the clever ideas you have thought of.
Welcome to the world of IOM racing, you don`t have to be mad but it helps.
Good Luck,

[Graham_Snook]

Thanx for your kind words IanHB,

At the moment The TC is next to me and I'm working away slowly on finishing the bits that I had to rush, so the kitchen is again full of dust and in about 30mins will start to smell of epoxy!

Just got to find a way to cant the keel forward a fraction and buy a few more fittings

I am very happy with the way she has come out...I haven't skimped on the building and she's still under weight which I had my doubts about at some points...that and the realisation she was 2mm too long! only to go back and measure on a surface rather than running the tape over the deck which was giving the extra 2mm! so with much relief I made a plug for the 10mm bumper

[mark dicks]

Graham
glad to see there is sailing at clapham again, i am still a member of clapham myc. as previous replies, weight distribution does not matter that much as long as you get design floating on designed waterline. let me know how it goes over the season
regards

Mark Dicks
Triple Crown Designer

[Graham_Snook]

With the angle of dangle now correct, and 250 grammes of plastascene ballast just in front of the keel box she now floats on her lines - well, as close as I could see from the shore without asking for help from the passing geese

I had a few problems with interference which happened because I ran the wire up the backstay, but it went when it was left dangling on the deck.

We had some breeze at the weekend, in the gusts it was probably the top for an A Rig cos she flew away with spray spitting from the bow, then throuoghly burried her nose and flashed her bum at me!

I'm still learning how to sail, but she can really shift when I get it right, and really hates it when I get it wrong! In spite of the burried nose and being over pressed the batteries lasted longer than I could in the bitter wind (and she didn't let in a drop of water inside). It was the weekend for the 6M's so I didn't get direct competition and could only just keep up, but their tatics are far superior to mine so when I slipped up I was left behind

I've still got to get used to the fluky winds (and the shallow patches) so the next step will be some sort of windex, but I was just glad to get her on the water.

It looks like I might have started something, (being a new member with a Triple Crown) Some of the other members are threatening to dust their TCs off....Oh lordy what have I started???