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daydream sailor 01-09-2013 02:19 PM

reducing draft depth ?
 
I was just wondering if there is a way two take a keel with a draft of six feet or more and turning it to a shoal draft for going into shallow areas,can a keel be cut and shortened, why ? why not?, just something i was thinking about, thanks.

kd3pc 01-09-2013 02:23 PM

Re: reducing draft depth ?
 
it depends on the boat, and the doing so should not be taken lightly. Some boats are easy...they were designed with a shoal draft and a deep keel, just swap one for the other. Other boats, the design and structure of the keel are paramount to the performance of the boat, as well as the safety.

If you can discover which boat and what you want to do, an engineer/builder of the boat in question can help with the project. Not cheap either way. A reputable shop is of utmost importance after the engineering is complete.

Others will chime in, I am sure.

chucklesR 01-09-2013 02:26 PM

Re: reducing draft depth ?
 
That last couple of inches of keel is where the most work in ballasting the boat is (weight lower is more effective than high).

So, sure. If you reduce sail by about 50% or more and otherwise ruin the boat or turn it into a displacement trawler.
Keel depth also affects pointing ability into the wind.

Naval architects crunch a LOT of numbers to get the keel right. Noodling with a pencil on napkin is not how to do it.

eherlihy 01-09-2013 02:39 PM

Re: reducing draft depth ?
 
I too had considered this while boat shopping. The conclusion that I arrived at, after pestering a bunch of people and companies (like Mars Metals in Toronto) is this:
The best and most cost-effective way to decrease the draft of a used boat, is to buy another boat with a shallower draft.

pdqaltair 01-09-2013 02:42 PM

Re: reducing draft depth ?
 
Quote:

Originally Posted by chucklesR (Post 973066)
That last couple of inches of keel is where the most work in ballasting the boat is (weight lower is more effective than high).

So, sure. If you reduce sail by about 50% or more and otherwise ruin the boat or turn it into a displacement trawler.
Keel depth also affects pointing ability into the wind.

Naval architects crunch a LOT of numbers to get the keel right. Noodling with a pencil on napkin is not how to do it.

The right answer is going to be "sell the boat and buy the one you need."

Chuckles last sentense is dead on; you will change the lateral plane, CG, pitching moment, righting moment... everything. If it can be done right, it will cost what the boat is worth. Better to exchange.

denverd0n 01-09-2013 03:43 PM

Re: reducing draft depth ?
 
Quote:

Originally Posted by eherlihy (Post 973077)
The best and most cost-effective way to decrease the draft of a used boat, is to buy another boat with a shallower draft.

Worth repeating, about eleventy-billion times!

Unless you have some really unusual requirements, it will practically ALWAYS be cheaper, easier, quicker, and safer to just buy a boat that is suited to your needs in the first place, rather than buying a boat that is not, and then planning to modify it.

Resolute_ZS 01-09-2013 03:52 PM

Re: reducing draft depth ?
 
Just playing devil's advocate, if you have a mass-produced boat that came with both options from the factory (e.g. a Catalina 385), would that make the problem any easier?

(Don't get me wrong... I fully agree with chuckles!)

rugosa 01-09-2013 05:27 PM

Re: reducing draft depth ?
 
All previous posts are on the money. I sail on a boat that PO switched from standard fin keel to shallower draft with a bulb added. I'm convinced it was done on a restricted budget with little or no consultation with the designer/builder. It was also designed for centerboard construction. I've sailed the same model with the standard fin too.

Up side - you get shallower draft - but no matter where you go, you are bound to touch bottom sooner or later

Down side - reduced pointing, compromised steering in heavy wind, a one-off boat with diminished resale value. We've priced out a keel swap - :eek::eek::eek: $10,000 (or more)

IMHO - find the boat with the draft you want. Go sailing.

Jeff_H 01-09-2013 05:31 PM

Re: reducing draft depth ?
 
Quote:

Originally Posted by Resolute_ZS (Post 973125)
Just playing devil's advocate, if you have a mass-produced boat that came with both options from the factory (e.g. a Catalina 385), would that make the problem any easier?

(Don't get me wrong... I fully agree with chuckles!)

Swapping the keels even in stock models is usually very difficult and expensive. Even in popular productions models the shoal draft versions often have a different keel root, bolt pattern and structure than the deep draft versions.

Like everyone said, "Fogedabowdit" just but the boat with the draft you need....


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