Join Date: Dec 2004
Location: Portugal, West Coast
Thanked 89 Times in 73 Posts
Rep Power: 10
Re: Bob Perry's take on Wolfenzee's dream boat
Originally Posted by bobperry
The premise was that you could build a more efficien( better performance) keel with iron than you could with lead.
To retain the same VCG of the keel the iron keel would have to have a much bigger bulb and a lot more frontal area I also think the fin portion of the keel would have to be bigger so even more wetted surface and frontal area is added.
It does not make any sense and I don't give a rip who did the study.
Think of it this way. If an iron keel could provide "better performance? why does every serious racuing boat in the world use lead for ballast. If spent uranium not not illegal for racing keels they would use that like they did back in the earkly '70'. It's denser than lead.
Open you eyes, not another book, the answer is easy to see in any boatyard. The more dense material gives the designer more freedom of design. Bulbs are slow. They cut into the clear span on the fin and reduce apparent aspect ratio. They add wetted surface and frontal area. Bulbs work because the allow for a very low VCG. This is far easier to achive with the more dense material.
For the third time I say that I agree with you, as certainly the authors of the study. It is evident that a keel with a bulb made of lead is more efficient than an all iron keel, assuming the same shape. That was never the point.
you say that :
"The premise was that you could build a more efficien( better performance) keel with iron than you could with lead."
but you are mistaken, they did never assumed that or wanted to verify that possibility. In fact the lead fin keel was only there for comparative purposes. They were studding basically different types of bulbed keels.
The fact that they had found that in some circumstances a torpedo iron keel
could be more efficient than a fin lead keel
was accidental and that is only valid to a fin lead keel versus an iron torpedo keel.
It is evident that if both keels had the same design, one in lead and other in Iron, whatever the design the lead keel would be more efficient (for the same RM) since it would have a lesser volume and a smaller drag.
what the study was aimed at was:
"The aim of this project is to evaluate four different keels and determine which one has best performance upwind. "
and about the keels and regarding the use of lead on the fin keel:
"The four keels should have the same righting moment in order to be comparable. This means that the static moment of the yacht which counteracts side forces from the sails should be the same. In the
redesign of the T-keel, this righting moment has to be kept constant. For an easy comparison between the keel designs the draft will be kept constant as well, and the fin size and shape will be identical between the bulb keels. ...
Keel 1 (Fin keel) was used only as a comparison for the other keels. It does have the same righting moment and maximum draft, but in order to fulfil this it had to be designed to be made of lead instead of cast iron as the other keels. This implies it will have a comparably smaller wetted surface, and consequently the drag forces will be smaller. The effects of these aspects were expected to occur in the results."
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.