Anybody out there!

[growjd8888]

sorry but im not familiar with the term "flession"

[matthias72]

Sorry I mean "flexion"

[k1w120]

Very good work .... following with interest.

Matthias means "flex" he would like to know when you hold the head of the keel fin to work bench, how much flex do you have in the fin.

Cheers Alan

[growjd8888]

Thanks for clarifying kiwi.. Thats a great question..I felt uncomfortable with my first keel which was made of poplar and 2 layers of fiberglass, laid in fiberglass resin.

These are pics of my first keel under flex.

I just coated my keel with a layer of resin so untl it is coated 2 more times and fully cured i cant test the flex of it,
- new keel is 2 layers of fiberglass and one layer of 5.8oz 2x2 twill carbon fiber, all laid in epoxy resin

I also diaper wrapped this keel fin and bulb together rather than laminate my fin and attach bulb later using only glue.

[k1w120]

Not knowing the construction technique of your keel fin it is very hard to comment, but it looks to roughly 40mm deflection, which is quite a lot.

There are different ways of making a stiff fin, some wrap 160-200 gsm carbon fibre with one layer at 45 degreeä's to the other (no fibreglass) others like myself, insert 2-3 carbon tubes 2-6 mm (depending on profile) along the length for the fin evenly spaced apart & set in channels cut into 3 x 2 mm balsa wood core strips, then sandwich each balsa layer with 100 gsm carbon and outter layer with 100-140 gsm carbon fibre, requires lot of prep work, but result from my short experience is stiff fin with 6-8 mm deflection.

Or you can make a mould and use stiff foam core cut to fin profile & insert diagonal cross braces inside the foam core and then sandwich the fin with carbon fibre. I'm sure there are other techniques also, but "one" of cretria of making good keel fin is to have the minimum possible deflection as possible as it helps with having the best possible righting moment, the other is keeping your rig a light as possible.

Small hint: Epoxy does not add any stiffness - ONLY WEIGHT - the function of the epoxy is purely to act as binder of the cloth your using, once the cloth has reached saturation any additional epoxy is just wasted weight.

Congratulations on your mast, very nice, just one layer carbon too many (weight) but excellecent work !

I'm interested in how you came to the idea of the bulb shape that you have ?

Cheers Alan

[matthias72]

The 40mm flexion may be due to the 3200g bulb weight, out of class rules?

[k1w120]

Hi Matt, Yes you are right, I never looked at the bulb weight ...but see in pic above fin & bulb and toatl weight at 3,370 grams before extra epoxy coating was applied ...means have long LWL with boat sitting lower in the water or was additioanl BWL displacement added to the hull ?

Maybe just my thinking ... but I'm imagining when you add the combination of possible hull siiting below water line (too heavy) and the interesting bulb shape ...this may result in the boats tendency to submarines at speed ...I thinking upwind !! not downwind which would be even worse still, unless it was tilted upwards ? ... but there is always some reasoning behind logic

[matthias72]

Hi Alan, this is a hard question.
Sailing upwind, It depends on wind intensity. If hard, it is sufficent to push to the LWL max boat speed at the same, also if the boat is more heavy and it moves a major water quantity. On the same time the major bulb weight allows a better performance so at the end the boat could is faster. Instead the major mass helps to break the weaves.
Of course you have a worse downwind performance, but not always: if the wind is heavy, also downwind the wind is sufficent to push the boat to its speed limit, so yor performance could be the same and you don't loose speed.
The limit is the hull height: if the water arrives to the bridge, the resistences increase.
In case of middle/light air, the light weight boat could have an advantage because the wind force is not sufficent to push to the LWL max speed limit the heavy boat cause its major resistence.

[k1w120]

Yes I agree a higher bulb/boat weight ratio is always a good thing, providing the boat has been designed for the changes ...

[matthias72]

Exactly! But not if you sail in light airs!!