modifying a boats keel

[manos]

Hellow,
I was thinking the subject of changing the centerboard of a double ender,(I was having in mind Mr Oughtred's boat Tirrik),
to a full keel with external ballast (something like haven's 12 1/2 full keel).Is this possible?What may be the diference to the behavior of the boat espesially in windy contitions?Is it going to be more stable or...?
In my mind a deep full keel gives the sense of a "small ship".

[JimD]

Greetings, and welcome to the forum, manos!

Don't know much about Tirrik but what you are proposing would be a major change to any centerboard design. Now might be a good time to read a good book on sailboat design so that you may better speak the language of naval architecture and gain a more complete appreciation of the many issues at stake. Then take your ideas to the designer. The more research you have done and the more it sounds like you are serious and know what you are talking about the more likely you'll be to receive a favourable response, I would think. Not presuming to speak on behalf of others but it wouldn't surprise me if Mr Oughtred replied that the boat's stability and performance have been painstakingly designed for the centerboard and to find another boat if a full keel is what you really want. Just my humble opinion which often turns out to be wrong. Good luck!

[johngsandusky]

I agree with Jim. Don't add a keel, find a keelboat that suits. Some conversions work out, others do not. It would be a shame to go through all the work of building her to find her performance unsatisfactory.

[Thorne]

As above, find a boat you like AS IS, buy the plan, build to the plan, no worries.

[Boatmik]

Welcome to the forum!

What you are suggesting is a

Major, Major, Major change.

Don't do it unless you really know what you are doing and personally I think it is impossible given the displacement and hullform of the existing boat.

The Tirrik's weight is in the 250lb range - add a person or two and you are probably looking at a displacement of 600 lbs.

The H12 1/2 comes out at a displacement of 1400lbs.

I suspect adding a keel to the Oughtred would make it a submarine - it would have the weight of a much bigger boat but no more volume in the hull to get it up and over waves.

And at the moment it is a wonderful rowing boat too - and you would lose that altogether if a long keel was fitted - too much weight and wetted surface.

If you like Oughtred's approach (and his plans are much better than just about anything else going) and want a keelboat then consider a Wee Seal - you could always make it open like the Herreshoff.

But you would need to speak to the designer for even a modest change like this.

Have a look here to see what happened when someone second guessed a designer and the cascade of problems it caused.
http://www.storerboatplans.com/Faq/stretchshrinkdesign.html

Boatmik

[manos]

Thanks all.
My question was hypothetically and I understand that a change like this will affect to the behavior of a boat.I know nothing about boat designing
and it is not my intention to make that modification on Tirriks hull.The examble of Haven was not the best one,(Atkins Valgerda is closer to what
I had in mind),I just wanded to know if something like that is possible and
its affection to the boat.The only change I am going to make to the plans
of Tirrik is to make the boat fully decked.
I'd like also to ask how can someone improve the steadiness of a boats
movement(make it less tipy) like Tirriks size?Any articles to read?
Thanks again and excuse my bad English.

[Boatmik]

Hi Manos,

No problem with your English at all.

With some of the bigger Oughtred boats of this style the builders have added ballast - not a large quantity - just to give the boat a bit more safety when cruising offshore.

You can probably find out about that here
http://www.mavc2002.com/cyforum/index.php

But in general if more steadiness is required choose a
1/ Bigger boat
2/ Wider boat
3/ Heavier boat
4/ Boat with ballast in the hull or keel

You don't need ALL these qualities in the boat you choose but the more the boat you choose goes in these directions the more steady it will be.

One of the steadiest boats for it's size I have sailed is the Bolger Oldshoe. I'd make be prepared to make quite long coastal passages in this tough little boat.

And it has a feeling of space inside much greater than its size.

Here is an article I wrote for a magazine once. (http://www.ace.net.au/schooner/oldshoe.htm)
Note that the picture at the top shows the one I sailed - the builder had extended the sides forward so the bow was pointed.

And here is a thread on building one (http://www.duckworksmagazine.com/01/articles/old_shoe/)

And you can be ready for sailing in minutes and is very easy to build.

It is 12ft long with a long keel.

But lots of people won't like the look and will choose something else more complicated.

By the way you can't put a keel like this on any boat and expect it to work well - the keel is matched to the hull.

[johngsandusky]

Even a rowboat or a canoe can be made more stable by adding inside ballast. If you build an open or small boat and it seems unstable, try adding water jugs or rocks to see if you can improve it. If you like that, replace them with metal ballast if you wish.

[Chan]

Actually the haven 12 1/2 is Joel Whites centerboard version of the herreshoff.

[willmarsh3]

Have a look here to see what happened when someone second guessed a designer and the cascade of problems it caused.
http://www.storerboatplans.com/Faq/stretchshrinkdesign.html

Boatmik

That builder is lucky that the designer helped him correct for his builder mods. Some designers will leave the builder no recourse but to start over. Actually, I think the latter may be the best bet because the design is more established and most likely safer.

Also as Ian Oughtred designs beautiful boats, making significant builder mods would most likely hurt their resale value.

We'd all like to see what you select and build.

Will

[Boatmik]

All good points willmarsh!

MIK

[JimD]

...Atkins Valgerda is closer to what
I had in mind...

A while back there was an interesting discussion on Valgerda and the benefits (or not) of the addition of the ballast keel. I was among those who thought it was a good idea and went a long way towards turning a small fish boat into a stable recreational boat. Why not build one?

http://www.boat-links.com/Atkinco/Sail/images/Valgerda-1.gif
http://www.boat-links.com/Atkinco/Sail/images/Valgerda-3.gif
She's a beauty of a little open boat and construction ought to be very straight forward.

[manos]

thanks,
I will go with Tirrik boat as soon as I repair my Acorn 10'2''dinghy.I lost her in a 8-9 beaufort wind contition one night.I left the boat at the beach near to 15 metres.The waves took her in their arms .A week later coastguard inform me that the boat was found about 1 mile away ,near the seashore
(100 metres),upside dawn and half buried in sand.The depth at that point
was less than 1/2 metre.I've got work to do.:mad:

[JimD]

Sorry to hear you lost your Acorn. A steel plate centerboard can be a very good way to lower the center of gravity and add some stability. Something to think about for the Tirrik.

http://www.duckflatwoodenboats.com/designers/oughtred/TirrikGunterSloop.jpg

[JimD]

Pics of a Tirrik:

http://www.grapeviewpointboatworks.com/images/tirrik/tirrik_rigged.jpg

http://www.grapeviewpointboatworks.com/images/tirrik/completed_interior.jpg

http://www.grapeviewpointboatworks.com/images/tirrik/interior_aft.jpg

http://www.grapeviewpointboatworks.com/images/tirrik/tirrik_rudder.jpg

And a link on building her: http://www.grapeviewpointboatworks.com/tirrik_intro.html

I can see now that it is quite a different boat from Atkin's Valgerda.

[manos]

JimD thanks again for your help.I've already made the centerboard from a piece 3.5mm stainless steel and two plywood cheeks with holes to the lower point for lead.The holes are big (like A4 paper size).The board weights 13 kgr. and I have not put the lead yet.One layer of fiberglass cloth , epoxy and I think it will be ok.If not I think lead pigs is a good solution.
Thanks.:)