Transom Extensions

[Epicurean]

Two years ago we went to the Outremer factory in Canet-en-Roussillon and was told that Outremer had extended the transom on the 45 by 4 feet, I believe. They said it was a large improvement. (They also said they wouldn't be calling it an Outremer 49.) That seems a very common thing to do. Are there any contributors who can share their experiences? How much improvement was realized? Are there any down sides? How much did it cost, if it was done after the boat was purchased? How is it advantageous? Are you satisfied that bit was worth it?

[thinwater]

Yup, I stretched my PDQ 2 feet.
* DIY. Not terrible, but you better be good at glass and understand the engineering.

* Yes, it was worth it.
* Boarding is much better. Performance improvements are mostly too subtle to measure objectively. Pitching is reduced and top-end speed is increased.


You can search my blog for details.

Sail Delmarva: Better Boarding--Extended Transoms
http://sail-delmarva.blogspot.com/20...s-process.html

[Epicurean]

That was great! Thanks.

I read your blog post and it was very good,too. In it you said any small speed increase would be at lower speeds, here at higher. Also you said pitching improvement was too small to notice. Here you say it's reduced.

The bottom curve is up at the transom. Following that might bring them somewhat out of the water. Any idea if that is a bad idea?

I'm also getting older. The boarding function alone makes them worthwhile.

I've fiberglassed but I'd hire someone, probably.

[44'cruisingcat]

How much improvement transom extensions will produce really depends on the existing setup.

If your current transoms are wide and deeply immersed, you can see good gains.

[thinwater]

Originally Posted by Epicurean

... The bottom curve is up at the transom. Following that might bring them somewhat out of the water. Any idea if that is a bad idea?...

In fact, they are 3 inches out of the water at rest. But as soon as the boat starts moving, the transoms sink, as you know. I think the main consideration is to follow the existing keel line, without compound curvature; you want a clean exit without increasing suction.

Yes, how much difference they make depends on the original boat, which is why my comments were vague. 44 is correct. They ONLY make sense if the original hull form was too short. My original transoms wee barely immersed (only when loaded) and not wide, so the improvements were modest. However, taken with modifications to sail plan and keel design, the total improvement was considerable.



For example, they help speed MORE with a full house and a cruising load then when I'm day sailing light by myself. They help with load carrying, reducing the extent to which minor overloads make things worse.

[Epicurean]

How do they help with load carrying? There can't be that much buoyancy in them. I would think that by increasing the waterline they would help and also help a little to prevent pitching. Just guessing

[Dan GB]

Originally Posted by Epicurean

That was great! Thanks.

I read your blog post and it was very good,too. In it you said any small speed increase would be at lower speeds, here at higher. Also you said pitching improvement was too small to notice. Here you say it's reduced.

The bottom curve is up at the transom. Following that might bring them somewhat out of the water. Any idea if that is a bad idea?

I'm also getting older. The boarding function alone makes them worthwhile.

I've fiberglassed but I'd hire someone, probably.

Mine was extended by previous owner before I got it, from 42' to 45'. I was told it they were delighted - they mentioned pitching and overall speed.

I like the access. And it makes a great little level platform to stand on. And it improves the look and lines of her in my opinion. They also did a beautiful and fair job.

I dislike losing the kick up rudders which basically got buried in the extension.

[smj]

Our old Seawind 1000 before and after transom extensions.

Added speed but more importantly drastically cut down on pitching which increased the speed. Every time I see an older Seawind 1000 without transom extensions I wonder why. They were that worthwhile.

[owly]

Originally Posted by 44'cruisingcat

How much improvement transom extensions will produce really depends on the existing setup.

If your current transoms are wide and deeply immersed, you can see good gains.

Transoms on a cat should never be immersed as far as I'm concerned... That's a huge amount of drag. An immersed transom screams "overloaded" to me. I'm really not sure why a reverse transom is more desirable than a well designed boarding ladder anyway. To me a reverse transom is a way to bring the waterline together beneath the transom, and has little value beyond that.



H.W.

[sailjumanji]

Originally Posted by smj

Our old Seawind 1000 before and after transom extensions.
Attachment 180430Attachment 180431
Added speed but more importantly drastically cut down on pitching which increased the speed. Every time I see an older Seawind 1000 without transom extensions I wonder why. They were that worthwhile.

Plus look at the ease of boarding from the side of the stern, vs aft boarding.

[smj]

Originally Posted by sailjumanji

Plus look at the ease of boarding from the side of the stern, vs aft boarding.

No doubt an added plus.

[thinwater]

Originally Posted by Epicurean

How do they help with load carrying? There can't be that much buoyancy in them. I would think that by increasing the waterline they would help and also help a little to prevent pitching. Just guessing

They eliminate transom dragging turbulence by extending the keel line aft and upwards. They also create a longer water line. Combined, these neutralize most of the effects of increased weight. No, they don't add much buoyancy, but they do modify the hull exit for deeper immersion.


They also help when pressing HARD to windward. Most (even all) of the weight will be on one hull, which will press the transoms under, just as though she was overloaded. As a result, pointing improves.


A lot of the effects are minor but synergistic.

[catsketcher]

A good transom extension can make a world of difference and some good ones will not extend the keel line.

If your cat is overloaded then the very slight increase in volume in some transom extensions that follow the waterlines and keel line will be negligible in terms of flotation. The waterlines are narrowing and the keel line is pulling up and so the volume when extended aft is lessened.

I have had a few friends who have gone forward of the transom by up to 1.5 metres and reduced the keel rocker aft. This gives a huge increase in volume and does a much better job of increasing flotation aft. You can widen the waterlines as well, which makes more of a difference as well.

I have seen some cats which have had extensions on thin sterns which would have done very little in terms of flotation at rest or much under speed. Broader transoms can do well with a simple stick on extension but you may need to go forward, foam up the aft sections and redo the hulls aft sections as well.

cheers

Phil

[Seaslug Caravan]

Originally Posted by catsketcher

A good transom extension can make a world of difference............

Broader transoms can do well with a simple stick on extension but you may need to go forward, foam up the aft sections and redo the hulls aft sections as well.

cheers

Phil

Phil, as one who has dabbled in design you really need to explain the ramifications of adding buoyancy aft to an existing hull.

Great when the displacement is shared equally between the two hulls.
Not so great when the sailing loads place more displacement into the lee hull.
Remembering the whole reason for the modification was overloading in the first place.

[Sand crab]

There was an outfit in France that had made molds for Outremer bow modifications which would give a more modern vertical bow. They claimed this had many benefits which elude me now but it did increase the waterline by a few feet.
Pardon the thread drift from stern to bow.