Not really a 6M; but !!!

[Richard98]

My lockdown project boat is progressing well, thanks to a fair amount of input from members. 

Bought as a planked, scaled down, Moby Dick design and being hacked about by me to make a sort of "what if" 6Metre yacht.  What could a 6M be if not quite so constrained by sail area, keel depth and hull contorting measurement rules. NOT intended as any criticism of the 6M, which is a lovely class to look at, just an exercise in what could be done.

I have removed 0.5Kg of internal structures /deck. The original fin, rudder & skeg and 7Kg internal ballast also lopped off.  A new c/f keel and rim tab plus an old One Metre rudder are the new external appendages. The new deck has ended up looking like a Swiss cheese as I thought of additional areas that may require access as things progress. A pattern has been made for a 7Kg ballast, which is intended to interact with the trim tab and, hopefully, the hull to increase effectiveness. For this reason the main fin section is just a simple aerofoil .

Thinking of sail plan now and aiming for 0.8-0.9 sq M. Maintaining the same ratios as typical 6M, also One Metre; which is interesting. Really want to go high aspect, but aware of keeping a sensible mast height. Substantial roach in order here, like the Merlin Rocket main. 

Here is the main point of this missive.    Does any one have any ideas on the project that they would like to see ?  Any comments on rig that could give me a steer on configuration.

Thinking carbon mast, maybe in two parts. No spreaders. Fractional rig with aforementioned main.  I like sleeved, fully battened mains though.

All comments / suggestions welcome and thanks to all who have already guided me.

 

Richard

[Richard98]

Progress:

Rigged up and just awaiting the ballast casting. This is a planform type intended to improve the efficiency of the keel in association with the trim tab.

Have reduced trim tab area after further calcs.

 

[Mike Ewart]

Looks nice but why didnt you make it measure as a six or an A the true test of any performance is in comparison to others by an approved measuring system

[Richard98]

Thanks Mike, for you comments, that have been a great help and your question here.

I love the overall impression of the 6M, but wanted a boat that made real use of the size and provide an exciting alternative to my One Metre. I ploughed through the 6M rating formula and ended up with a sail plan comparable to a "Star yacht". The crippler was the draft penalty.

I saw no point in building a boat of this size with such a tiny righting moment. Increasing the fin depth seems easy to do; so I did it ! Actually more than  doubling the righting moment for what is still a modest draft of 340mm. I also selected a ballast weight of 6Kg to make the whole thing more manageable at the waters edge.   Part of the problem with the "classic" shape is the poor ballast ratio and sail area penalties . 

The boat has a respectable 1.0 sq m of sail on a shroudless carbon mast ( for simplicity) and should do justice to a lovely hull. This sort of explains my thinking and the reason why the excellent 6M class is not for me. One amazing plus though; The boat sits on its own. Can't do that with the One Metre !

 

[Richard98]

Sailing !!!

Second outing, after a few tweaks. Sails very pleasantly, perfectly balanced and very responsive. The trim tab works but would need to sail in company with a similar boat to gauge efficacy. Possibly not enough wind to detect any improvement beyond that of a biased imagination. The un-stayed carbon mast makes rigging really quick and the boat much easier to carry, with less to snag.

I would not like to carry and launch anything in excess of this weight ( just under 10 Kg all up) though. Can manage to carry to the waters edge in One Metre fashion; one hand on L/E of fin and other hand carrying the stand.

Next project ???

 

Edited August 28, 2020 by Richard98
additional info; weight

[tiggy_cat]

That looks lovely.   I know what you mean about weight.  My old A Class weighs 51lbs and while impressive, I am not sure that I am going to manage moving and launching that very often. 

Edited August 19, 2020 by tiggy_cat

[Richard98]

Legal rig ???

Just been re visiting the 6M rules after looking at some older posts on the subject of rigs. I know that the rule allows only one mast and my carbon un stayed mast is legal. However it appears that a pocket luff mainsail is not prohibited. 5.3.2 states that "double luff mainsails are prohibited" 

Why are no 6M's being rigged with un stayed masts and pocket luff mains ? 

Richard

[tiggy_cat]

On 19/08/2020 at 17:59, tiggy_cat said:

That looks lovely.   I know what you mean about weight.  My old A Class weighs 51lbs and while impressive, I am not sure that I am going to manage moving and launching that very often. 

May have solved that now

[Richard98]

Assume you back up to the water and launch off that ramp with the boat on a trolley. Neat. 

Richard

[Richard98]

Back on the water and I have realised that I love these big boats. So many different considerations compared to the full waterline, slimmer boats.  I now have a B rig and I attach pictures for comparison. Some will recognise the origin of this B rig. That gives me 1.0sq M and 0.6 sq M respectively on the same luff length of 1720mm.

I realise that the boat is way too stiff and have reduced the ballast to 5Kg, which brings the overall weight to <8kg.  The A rig brings the boat up to hull speed very quickly and it needs to heel to bring in the free additional waterline provided by the overhangs. Hence the ballast reduction  Changing down to the B rig takes 2 minutes and is soooooo easy with the shroudless rig. Therefore the boat remains in its speed groove better. I anticipate an IOM B rig as the C rig for this boat and this combination should see it sailing consistently within its "sweet spot" 

Also going to reduce the trim tab area a bit more, although I have still not been able to evaluate it against another boat yet.

The boat draws considerable attention due to its impressive size and is proving a joy to sail

Richard