Tahiti Ketch

[Hugh McCormack]

Can anyone tell me how this Hanna designed Tahiti ketch makes more headway than leeway with a keel this uniformly shallow (images & specs attached)?
Cheers, Hugh McC

[pcmm]

Easy...Don't go upwind!!

[Bowdrie]

When you're reaching and running in the trade winds you'll get a nice comfortable ride.
Going to weather in light air or a short chop is frustrating, but at least you don't have to "wear ship" like a square rigger.
The rigs have a low center of effort, and you can carry sail in surprisingly stiff conditions, you just can't point as high.
The list of long voyages by them, (and their ilk,) is substantial.
They are certainly not an "around the buoys" boat.

[Hugh McCormack]

Yes, I know they are world travelers, but one wonders about righting moment, and stiffness in a blow. Why such a giveaway to leeway and stability, i.e., overall ability to get from a to b in upwind conditions?

[boatman61]

Look at the date of the original design.. 1928 I believe.
That should give you a clue, if the specs are changed it ceases to be a Tahiti.
Its down to personal choice, if you want something that can double as a round the buoys weekend racer/cruiser buy a Bene or J Boat.. if you want a stable, comfortable cruiser buy a Tahiti..
A serious cruiser usually waits for the favourable weather.. I know I do, if theres a SW'ly blowing and I need to round Finisterre I'll sit it out in Viviero till the predominant weather pattern resumes regardless of the boat I am on.

[chrisr]

sounds like you are comparing a 100 year old design to modern stuff

yes, there is a lot of difference (more than most purists will admit to). old boats like this generate their righting moment by being HEAVY. they also don't need so much righting moment as the rigs are small and low so don't generate much heeling moment

they make less leeway than you'd expect because the deep full bodied hull gives them some grip on the water (to make up for the absence of a useful keel)

despite this, if you are not in a hurry, they can make comfortable cruising boats (just inefficient and deeply frustrating ones !)

cheers,

[psk125]

Chrisr's explanation makes it sound like the design doesn't go to leeward beacause there's too much drag for it to move in that direction. Could be.

[Bowdrie]

Like most designers, I'm sure that Hanna was doing his best, (within the constraints of his era,) to put 10lbs in a 5lb bag.
1, Making a hull with enough interior volume to carry the stores necessary for a long voyage.
2, Keeping the draft down to not only enable "gunkholing", but easy hull cleaning in areas with little tide, (not a lot of haulout facilities in 1928).
3, An easily handled and maintained rig, (remember, cotton/manila, and no winches).
4, A hull that would be more easily controlled by crude methods of self-steering.
And trying to do all that and more in only 30', (but it's a BIG 30').
I'd say he did quite well, and keeping the B/L ratio reasonable does help speed.
As previously posted, displacement in-and-of-itself is a large factor in stability.
If you want some fun, run the numbers/ratios against a Westsail 32, the original hull of which is a 1927 design by William Atkin, and used a ketch rig.

[Hugh McCormack]

I appreciate the comments.
From a wooden boat forum:
"The [Hanna Tahiti] boats built with a cement ballast keel tended to be a little tender...Concrete looses a lot of effectiveness because of its light weight. By itself it is only about twice the weight of water and it looses a lot because of its own buoyancy. I'd plan for an iron or even lead keel."

I suppose what's inside the keel matters most in this case. Hanna lived in Tampa, FL, and there was a sponge industry there, and southern American waters are usually quite shoal. But everyone seems to agree, these boats were workmanlike, seakindly, and ocean crossers.

[Brioche]

A deep fin keel operates mainly as a wing and thus depends on forward motion to generate life to reduce leeway. If a model fin keel boat is sitting still, it can get pushed to the side fiscally easily because most of the rounded hull is more or less streamlined for sideways movement, and the only resistance is the square footage of the fin keel. A long shallow keel has as much or more square footage, and added to the hull profile itself, plus its role in interrupting the flow of water under the hull from sideways movement, actually generates a fair bit of resistance. Think of the old square riggers that had virtually no keel. But as the boat sped up, it would not generate any additional lift through the keel, and would suffer badly from leeway then, while fin keels become more and more effective with speed.

[Hugh McCormack]

Yes, I'm pretty familiar with the hydrodynamics of fin keels, which is why Hanna's Tahiti and its relative absence of noticeable keel depth surprised me. But as many have remarked, this is a boat with a lot of wetted surface, fairly heavy displacement, and a full length of keel (shallow but the run of the underbody), and probably keeps her track well enough.

[NSboatman]

I had a Hanna Carol ketch- big sister to the Tahiti. Gorgeous boat, built in kyrennia on Cyprus, of African mahogany and gum/eucalyptus. 37’ long, 5’ draft, full keel double ended just like you stretched the Tahiti.

The original owner ordered the boat with a Frederick Fenger designed wishbone ketch rig, which put a LOT more sail area where it was needed. Very unusual combination, and took some getting used to- but that boat could take anything and be quite lovely and spritely to sail - as long as there wasn’t much chop. 2’ of chop and that big bluff bow would throw it everywhere.

Lived on and Sailed that boat about 10,000 miles offshore back and forth between the Caribbean and Nova Scotia for a good long stretch, and loved how comfortable and gentle the motion offshore was.

One particularly nasty Gulf Stream crossing in late November we were caught in the north wall of the stream in about 60kt nw’lies that kicked up an unholy crossed sea. Tiny storm jib sheeted flat and we had one hell of a ride downwind on deck. Down below, it was calm and serene, barely a sign of the chaos on deck.

Unbelievably comfortable motion, and always had the best sleeps on that boat.

Got a bigger (47’) Roberts steel cutter now (space for kids!) and yea, I do like sailing faster and being able to lunch through more chop, but honestly the motion on the old wooden Carol was better in most downwind conditions- which is what they were designed for.

[Fore and Aft]

Hugh McCormack who cares how well she sails. I have had some great sails on Tahiti Ketches. I never stepped onboard expecting a rocket ride. Its more about the romance and enjoying the slower pace of life. Very similar to owning a VW Kombi but with less break downs.
Cheers

[Hugh McCormack]

Fore and Aft,

Do you think I'd be chatting on about a Tahiti if I was after speed, or wasn't an incurable romantic? Her *relative* absence of a what we all see in our minds when we say full-keeled was all I was wondering about. And what little there is of one is encasing lead (not iron or cement) which is what I'd want for some stiffness. I won't expect more than 5kn avg., and will sail her as high as a close reach, and not expect more than she has to give.

Cheers, HMcC

[Bowdrie]

So, are you in the market for one?
There have been hundreds of them built over the last 85 years since they were published in Popular Mechanics in 1935.
Been built in just about any scheme one could imagine.
Perhaps the "closest" one in a fiberglass rendition would be the Dreadnaught 32.