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Old 18-03-2010, 21:52   #1
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Do Stern Extensions Make Much Difference ?

Its great to find some real world data to compare the difference between catamarans with and without stern extensions.

There's probably no better Guinea Pig to observe than the Seawind 1000 and the newer 1000xl with the stern extension.

At the recent Morten Bay Seawind regatta we got to sea 5 of both variants compete.

The results can be viewed at http://www.venturer.com.au/system/fi...%20Results.pdf

From the elapsed time we see that the average's for the two variants are within 4 minutes for the first race and around 2 minutes different for the second race.

The 1000xl being faster in each case. Considering that the 1000xl are newer , with the associated newer gear etc, the difference appears pretty small.

If one ignores the fastest and slowest boats(either lucky or inexperienced sailors) of each variant little effect is noted on the averages.


Interesting?
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Old 18-03-2010, 22:31   #2
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I scarcely know what to say...

Your assumptions have far too many additional variables and too small a sampling to be able to draw such conclusions. And why does this matter to you?
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Old 18-03-2010, 22:37   #3
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Do stern extensions make much difference?
YES

At least they did on my last boat and on any vessel that has had a step job that I know of.

Increased speed
Less hobby horsing
Less squat under motor
Able to carry (larger) dinghy without squatting
Ease of getting on and off vessel
better aesthetics.
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Old 19-03-2010, 01:30   #4
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Quote:
Originally Posted by cat man do View Post
YES

At least they did on my last boat and on any vessel that has had a step job that I know of.

Increased speed
Less hobby horsing
Less squat under motor
Able to carry (larger) dinghy without squatting
Ease of getting on and off vessel
better aesthetics.
Absolutely right , I can agree with every point here , having extended my sterns for these reasons .It was SO worthwhile . Well put catman !
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Old 19-03-2010, 03:11   #5
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The Seawind extensions seem very practical, not the least is the side entry step which makes boarding from a dinghy easier.

I believe they changed the design after getting feedback from owner/racers in Miami who were making this change and reporting positively about it.

It obviously convinced them that the change was worth making.
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Old 19-03-2010, 03:56   #6
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I find myself with a niggling thought. I wonder if Bayview owns a Seawind without the extension!

P.
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Old 19-03-2010, 06:11   #7
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By merely extending the aft sections of the hulls may improve buoyancy but it also changes the position of the mast relative to the LWL.
When I extended the sterns on my cat, I also had to extend the bows to retain balance. However I forgot about the spars and rigging, which were now too short relative to the longer boat. Mast and all standing rigging had to be extended. New sails, ALSO.
The Changes made a significant difference to the water line and to SOG.
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Old 19-03-2010, 09:27   #8
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We have just added 4' stern extensions to our new to us Seawind 1000. Most notable is the lack of a wake of the stern as opposed to before. This to me means less drag and more speed. Also under power the stern stays above the water. The extensions to me make the boat look a lot sleeker and a ton easier to board from the dinghy. I didn't have a chance to sail the boat alot before the extensions but with the extensions and the new screacher she sails very well in light wind.
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Old 19-03-2010, 10:23   #9
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I have never sailed an extended cat, but have sailed a bristol 73 that was lengthened to 83'. The unintended consequenses IMHO outweighed the advantage that a dinghy garage added. By moving the stern aft, the rudder appeared to be too far fwd now causing steering problems and strange balance issues. For all I know that may just be on this particular boat. Just food for thought.
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Old 19-03-2010, 11:01   #10
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Sailmonkey, I guess the Bristol is a monohull. Well, that's just how those are. They do have strange balance issues. Like how they heel over crazily. But for some odd reason they have utilized an alternative stability concept by putting a lot of heavy metal in their keel. Even though they behave weird and uncomfortable, they are relatively safe, if you know how to swim....

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Old 19-03-2010, 11:06   #11
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No matter how much they cost, transom extensions appear to be the most economical solution to "Two foot-itis"

But the differences between the 1000's and the XL's in these two races are quite dramatic. That's a minimum of 3 minutes in 80. That's the difference between getting to your next destination before vs. after dark! It's a bigger difference that trading in your 1000 for an 1160! In other words, its a VERY big deal!

When I've run out of old stuff to replace on my PDQ, I will extend the transoms myself, following the suggestions of the designer.

Note to Monohulls: As you heel an extended transom boat, the waterline increases aft, delaying the stern wave. The CLR shifts aft as the keel and rudder become less effective Hence the stability and trim issues. Catamarans are less severely effected because they heel much less.
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Old 19-03-2010, 12:22   #12
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Quote:
Originally Posted by Stein View Post
Sailmonkey, I guess the Bristol is a monohull. Well, that's just how those are. They do have strange balance issues. Like how they heel over crazily. But for some odd reason they have utilized an alternative stability concept by putting a lot of heavy metal in their keel. Even though they behave weird and uncomfortable, they are relatively safe, if you know how to swim....

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LMAO..............
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Old 19-03-2010, 12:41   #13
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Interesting article in a UK sailing magazine a while back of a bloke who built a rather nice 38ft steel yacht. Having set off looking for blue water and sunshine he realised that the lack of a large lazarette to store stuff was an issue. So out she came in some desolate hot and dusty back water. He buys some local steel sheet, strikes up the electric welder and tacks 4 feet on the back end. Billiant, wish I could do that.

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Old 19-03-2010, 13:02   #14
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But you can Pete! Not all that different from welding, (except from being totally different). :-)
Either way, building it with foam sheets ("sheet" is maybe the wrong word?) you can shape it as you go too. The big first steps are to get to know the basics of FRP and then grind away the shiny surface of your pretty boat at the point where adhesion is needed. Steel boats often are not that smooth to start with, so adding some more in the same style is ok. Doing the plastic version on a boat with top quality finish, it's easy to make the part functional, but difficult to match the finish ang make it look like it belongs on that boat.
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Old 19-03-2010, 13:29   #15
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Current boat is fine, we have a sugar scoop stern which makes getting in and out of the dinghy a breeze at anchor. GRP not a problem, its just like making bread, mix up the ingredients in a pot and away you go. However learning to weld is one of those life skills I seemed to have missed out on. Thankfully there are no shortage of local welders who will do little jobs for donation to the coffee fund.

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