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 Post subject: Does my **** look big in this?
PostPosted: Sun Nov 21, 2010 9:08 pm 
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Location: United Kingdom
I'm running an experiment to try and gain some experience with the Maas style stern treatment. Its intended to be reasonably readily removable to bring the shape back to what it should be.


Last edited by jimc on Mon Jan 31, 2011 8:17 am, edited 1 time in total.

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 Post subject: Re: Does my **** look big in this?
PostPosted: Tue Nov 23, 2010 7:24 pm 
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Hmm, double checking the rules I think I may have to do some subtle shaping of the gunwhales to hit the 60mm min radius:-) Fortunately my sailing location makes an external rubbing strip almost mandatory so I can play games with that... Pay attention at the back there Champ...

[Later] Here is my usual diary type effort of what I've been up to.
http://www.devboats.co.uk/257stern/

[days later]
When I got to look at it again there was minimal rounding of the gunwhale join needed to hit the required radius. Although a 60mm radius circle looks pretty damn large, its much less of a challenge on about a 130 degree angle. I should add that the actual main structure of the hull is within the radius anyway, so its within the spirit of the rule as well as the letter. Having a sharp transition on the hull and a smoothed one on the rubbing strip would have been rather a dubious practice.


Last edited by jimc on Mon Nov 29, 2010 11:42 am, edited 1 time in total.

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 Post subject: Re: Does my **** look big in this?
PostPosted: Sun Nov 28, 2010 6:19 pm 
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I'm interested in your mast gate tube, or whatever you call it. I seem to remember a similar arrangement on the Maas canoes. I guess that the mast enters an oversize oval section tube with the gooseneck and kicker loads transfered directly to this and not onto the mast. How long is the section of mast that slots inside and where is the mast step located. More interesting how is it fixed?


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 Post subject: Warning - Essay!
PostPosted: Sun Nov 28, 2010 8:49 pm 
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colinbrown wrote:
I'm interested in your mast gate tube, or whatever you call it. I seem to remember a similar arrangement on the Maas canoes. I guess that the mast enters an oversize oval section tube with the gooseneck and kicker loads transfered directly to this and not onto the mast. How long is the section of mast that slots inside and where is the mast step located. More interesting how is it fixed?

The mast and the mast stump don't telescope: they are effectively butt jointed. .There is just a short piece of extra tube projecting about 10mm or 15mm from the mast foot as a tenon to ensure that it can't fall out, which is tapered. The tenon doesn't control mast bend in any way, but of course the compression down the mast tends to keep the two compressive surfaces lined up. The stump started out with the same internal diameter as the mast external diameter, but is sleeved to the same internal diameter to, I think, a bit above daggerboard case height. Both stump and mast are then stepped out at the mating surfaces by various collars glued on, so they both end about being about 10mm thick at that point. This area could be done better but it works OK. The main tube of the mast stump ends up on the inner skin of the the hull shell, but doesn't really rest on anything special there, just a tad of extra carbon. Its very throughly carbon taped onto both the transverse bulkhead and the fore and aft spine, so the loads are being distributed right through that structure. The bulkheads and spine of course have plenty of carbon taping onto the hull shell, so the loads are widely distributed. The shrouds are exactly at the other end of the bulkhead, there isn't the offset there is on a lot of ICs. The spine doesn't go right to the bow though. There's a cedar/carbon beam under the foredeck, about iirc 30mm * 7mm, but the bare shell was so spectacularly rigid forward of the mast that I really don't worry about forestay load bending the hull. The whole affair is rather strong if maybe a bit heavier than it might be: I'm sure its over engineered.

The mast is moderately different in setup to most too. The rig would probably suit someone of Colin Newman's dimensions better than me, but its the tube I had! Its based on a Superspar 5515, so is more flexible than most: its 55mm * 1.5mm as opposed to the 55 * 2mm of the "standard" 5520. However the front half of the cross section is beefed up below the spreaders a good 1.5mm on the front face, tapering off round the sides, so its stiffer than a 5520 below the spreaders, especially fore and aft. From there the reinforcement tapers off to a tad above the hounds where it stops. Spreaders are raked back and rig tension is moderate - sufficiently so that tension on the leeward side is negligible with the rig depowered with a lot of mast bend. I don't have adjustable shrouds: whilst I freely admit that it would be better, especially offwind in the light, at the moment I think there's more speed available to me by just concentrating on sailing with better trim, sheeting and so on than there would be freeing off the shrouds. For similar reasons I don't change rig tension, there is plenty of depower available by blading out the sail above the hounds with downhaul and twisting off the top. The idea is that the rig is manageable and responsive rather than powerful. I do all my sailing inland where its very gusty, and I think that's the way to go at my rather moderate level of boat handling competence. The mast is I think much more free to bend than most because there are no lowers or deck level control and certainly much more mobile than the twin spreader Kiwi 12 footer rigs that it’s a sort of grandchild of... Without kicker induced bend there is fairly moderate lower mast bend anyway, most of which is put in by downhaul and wind pressure, although the spreaders put pre bend in when the tension comes on. The extra reinforcement on the mast is intended to make the mast bend go above the spreaders much more than below, and there seems to be a reasonably progressive increase in fore and aft bend from bottom to top. The sail is rather less than square topped simply because I didn't think the top mast would be stiff enough to support a more radical roach profile. I reckon I was right too!

Setting up the stump rig for a mast used with adjustable rake would be interesting. Its something I haven't tried because all my stump rigged boats have had fixed length shrouds.. I *guess*you would need to give a slight radius to the mating surfaces on mast and stump, and then greatly increase the width of the bearing surfaces in order to get the pressure load on the mating surfaces back down to something reasonable. Alternatively maybe a lateral mortice and tenon with a semicircular profile so it can rock fore and aft.

As for how well it works, well my club results are better this year than they ever have been, but of course I might just have learned to sail a bit better. Unfortunately I haven't managed to get to a single open. As you may have seen me say before, unless you actually get into boat swapping and two boat testing I've never really worked out a way to be sure whether Bill/Jane won because of his/her boat speed or in spite of a lack of it. We've surely all seen examples in one class or another of the Champion selling their boat and it immediately disappearing to the back of the fleet with the new crew on board.


Last edited by jimc on Mon Nov 29, 2010 2:20 pm, edited 2 times in total.

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 Post subject: Re: Essay
PostPosted: Sun Nov 28, 2010 8:54 pm 
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Location: United Kingdom
Some pics...

http://www.devboats.co.uk/257rebuild/images/j_bowfoam.jpg
This is as good as any for showing how the stump integrates into the structure. The styrofoam extension to the spine didn't survive: weight budget!

http://www.devboats.co.uk/257stern/misc/canoejoin.jpg
This is the join. This is the mk1, and the stump was a bit down on surface area. Its been tidied up since.

Mast bend. http://www.devboats.co.uk/257stern/misc/canoebend.jpg
This is the main that came with the boat, not the sail cut for the new rig.


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 Post subject: Re: Does my **** look big in this?
PostPosted: Sun Jan 30, 2011 5:48 pm 
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Location: United Kingdom
Image
Hit the water today, finally painted... Conditions F2/3, gusty, sailing poor - very rusty. Right arm and wrist aching so much can hardlytype...

OK, so how does it feel... Well, to be honest it makes a lot more difference than I expected. The stern wave is very obviously lower and flatter, so more pressure recovery going on I think. As Rob M predicted to me the bow is a good couple of inches lower when reaching, amazed its made so much difference. You can see the chine digging into the water some when the boat is heeled, this is especially striking sailing upwind with windward heel, which I tend to try and do. Water goes over the stern quite readily when heeled either way which is to be expected so more freeboard than a standard Nethercott is preferred. Or just keep the boat flatter of course. At least one other club sailor reckoned that the boat was noticeably quicker, and although it was good conditions for the Canoe which may have affected his assessment I think this change has added performance in that wind strength, but of course that was always where it was likely to gain. Lighter winds are likely to be a weakpoint, may be worse than I thought unless I try very hard to get weight forward as corner of stern is more likely to immerse than I thought. Stability... I didn't think it was more stable out there, but I do now I think. Was very rusty, had to slip of plank twice to avoid being teabagged, yet no real ropy tacks. Interesting to see what happens in breeze.

More pics and comments on the web page http://www.devboats.co.uk/257stern/, but to be quite honest the above is is the majority of actual content so far.


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 Post subject: Re: Does my **** look big in this?
PostPosted: Sun Feb 27, 2011 4:53 pm 
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Out again today. Three races, first f1 ish, second F2-3, 3rd a good F3. Running down to the start in the very light she felt horribly sticky. With sufficient attention paid to trim and heel angle things were bearable, but definitely feels slow in those conditions.
Sailed a **** poor first race and got the deserved handicap position. n awful lot of the race was pure displacement sailing. Once there was a reasonable breeze the boat felt OK, but probably slower than a standard Nethercott I would guess.

The wind perked up for the second pair of races, which were short back to back on a quadrilateral course. There was nothing else out faster than an RS200, so both races took much the same course, first round every mark, and a respectablish (for me steering) mid fleet result on handicap.

I'm now pretty convinced the boat is easier to tack with the extra stern volume. It was windy enough to be overpowered frequently, although not really enough that I had to get to the downhaul and blade off the top of the sail. In those conditions I think I'd normally have one or two poor tacks, but they all seemed to come off OK, if some better than others... Once up to a good planing speed I also think the boat is faster: the stern wake is spectacularly flat.


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