Anybody out there!

growjd8888
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Joined: 03/11/2009, 14:22

Re: Anybody out there!

Postby growjd8888 » 12/12/2010, 5:55

sorry but im not familiar with the term "flession"
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DSC00091.JPG
DSC00093.JPG
bit blurry but trying to show how the vacuum forces sharp corners with ease

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matthias72
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Re: Anybody out there!

Postby matthias72 » 12/12/2010, 17:08

Sorry I mean "flexion" :D
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k1w120
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Re: Anybody out there!

Postby k1w120 » 12/12/2010, 19:28

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
Posts: 69
Joined: 03/11/2009, 14:22

Re: Anybody out there!

Postby growjd8888 » 13/12/2010, 0:41

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.
Attachments
DSC00095.JPG
keel was clamped so the flex starts where the fin exits the hull
DSC00096.JPG
level was held on top of keel to show it starts level
DSC00097.JPG
DSC00098.JPG
new keel with one finish coat still drying
DSC00099.JPG
peelplys rough, dull texture makes finish coats sag much less and still allows look of CF to come back out

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k1w120
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Re: Anybody out there!

Postby k1w120 » 13/12/2010, 10:58

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

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matthias72
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Re: Anybody out there!

Postby matthias72 » 13/12/2010, 11:58

The 40mm flexion may be due to the 3200g bulb weight, out of class rules?
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k1w120
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Re: Anybody out there!

Postby k1w120 » 13/12/2010, 12:36

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 :D

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matthias72
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Re: Anybody out there!

Postby matthias72 » 13/12/2010, 13:01

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.
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k1w120
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Re: Anybody out there!

Postby k1w120 » 13/12/2010, 13:11

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

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matthias72
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Re: Anybody out there!

Postby matthias72 » 13/12/2010, 13:13

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