Do Stern Extensions Make Much Difference ?

[cat man do]

Originally Posted by Laidback

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.

How did you know that?

Was it something you found out by sailing the boat yourself after the step job was done or was it something that you were told to extract some more cash?

[44'cruisingcat]

Originally Posted by fishwife

I find myself with a niggling thought. I wonder if Bayview owns a Seawind without the extension!

P.

Niggling is right. Bayview is just trying to have a little dig at a member here who owns a 1000xl.

[bill good]

It might cost you more with the length increase in marina fees!!

Weight decrease is more the answer. Take off the extra "things" & try again.

Regards Bill.

[cat man do]

Originally Posted by bill good

It might cost you more with the length increase in marina fees!!
Regards Bill.

A lot of marinas charge in 10m to 12m and 12m to 15m brackets , so best to push it out but not over eh?

Anyway, the difference, if you really must stay in a marina is usually only dollars a day.

[Laidback]

Originally Posted by cat man do

How did you know that?
Was it something you found out by sailing the boat yourself after the step job was done or was it something that you were told to extract some more cash?

Cat man do, a pity that that you cannot refrain from personalizing your post.

But, for those members who are interested, I sailed my catamaran before and after the modifications were made. I assisted in the hull work, but did all the mast and rigging work myself.

[cat man do]

Originally Posted by Laidback

Cat man do, a pity that that you cannot refrain from personalizing your post.

Sorry you see it that way, it was not intended as you see it.

But, for those members who are interested,

I was interested, it is why I asked the question

I sailed my catamaran before and after the modifications were made. I assisted in the hull work, but did all the mast and rigging work myself.

Yes, but did you sail it after the step job was done with existing rig and no bow work done?

That was the question and would have been the true test as to what the differences are.

All the ones I have done and had anything to do with and have sailed on have not needed mast extensions, or new sails made or bow extensions done and they all sailed with a better feel with less pitching and therefore faster.

Maybe we were just lucky.

[Laidback]

I repeat " I sailed my catamaran before and after the modifications were made. I assisted in the hull work, but did all the mast and rigging work myself." Yes it was a true test, resulting in better pay load capacity, SOG, comfort and general performance - and to clarify further: it was not a step job.
The modifications and alterations to the hulls were approved by the designer.

[cat man do]

Originally Posted by Laidback

I repeat " I sailed my catamaran before and after the modifications were made.

Yes, I saw and acknowledged that but you did say that

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.

My question was, how did you know this?
Did you sail it first to see if the balance was out by doing the step job only- AND THEN pull it back out and do the bows as well after feeling the balance to be out?

or did you do steps and bow in one go as you were TOLD that the balance would be out, but hadn't actually seen or felt this for yourself?

[Laidback]

Cat Man Do,
Your posts are taking on the tone of an interrogation. Enough is enough.

[cat man do]

Originally Posted by Laidback

Cat Man Do,
Your posts are taking on the tone of an interrogation. Enough is enough.

You may see it as an interrogation, I see it as a simple question to qualify a comment that you made.

All I wanted to know was had you sailed the boat AFTER the step job was done but BEFORE the bow job was done and wonder why this question is so difficult for you to answer..

If you didnt sail the boat with ONLY a step job done, how can you claim with such certainty that the balance was wrong?

[Richard Harper]

For me the real advantages of the stern extension are:

Because the platform is only inches above the water line, you can surf right on to the stern platform after swimming, the boarding ladder is not required..
The stern platform is the perfect place to take a shower and not track salt water aboard.
It works great for cleaning pots and pans in seawater and then rinsing with fresh water.

[cchesley]

I don't think there's any case where a well designed and engineered extension on a multihull will have worse results. Boats always look better the longer they are, and are faster with the longer waterline. Adding both bow and stern extensions would be my preference for a more balanced look. You now have a longer (and relatively speaking, lighter) boat. There should be no need to add rig since the beam has not increased. The added weight of the extensions is minimal compared to what it would have been had the boat been designed to be that length originally. I suspect that seakindliness, speed and load carrying are all greatly increased with hull extensions.

As much as I love my MC 41, I often contemplate adding 2-3 feet on each end. I believe she'd be a better boat. Another benefit is that the hull length to beam ratio is immediately improved. I've come to believe that this is the single most important piece that contributes to performance.

I wonder what it'd really cost to do that........????

[Laidback]

Originally Posted by cchesley

I don't think there's any case where a well designed and engineered extension on a multihull will have worse results. Boats always look better the longer they are, and are faster with the longer waterline. Adding both bow and stern extensions would be my preference for a more balanced look. You now have a longer (and relatively speaking, lighter) boat. There should be no need to add rig since the beam has not increased. The added weight of the extensions is minimal compared to what it would have been had the boat been designed to be that length originally. I suspect that seakindliness, speed and load carrying are all greatly increased with hull extensions.

As much as I love my MC 41, I often contemplate adding 2-3 feet on each end. I believe she'd be a better boat. Another benefit is that the hull length to beam ratio is immediately improved. I've come to believe that this is the single most important piece that contributes to performance.

I wonder what it'd really cost to do that........????

cchesley,
When I decided to extend the sterns of my catamaran, it was because she was down on her lines, especially at the stern. So this was the first modification - it changed the sailing characteristics marginally, but improved motoring and payload, also the extremity of the stern hulls were now out of the water.

Having previous followed Lock Crowther's experiments with bulb extensions to the bows and to the success of French designers with their vertical bows (stems). This led to the second modification - adding to the bows, this improved both sailing, payload limits and comfort.

For the above mods, the cost of the materials ie :- Airex - fibreglass, resins and paint etc. did not break the bank - in comparison to the labour cost.

When it came to the mast and rigging additions, A section of mast extrusion was imported from Almasts Australia, this was inserted above the mast winches and below the spreaders. The standing rigging was upgraded from 8mm to 12mm. Because I was in Hong Kong at the time, the new sails were designed and supplied by Lee Sails.
This final modification made the real difference to SOG - now the cat could average in good winds 192 nm/p/d
Each and every stage of research, addition and modification made measured improvements to the boats payload, sailing, speed over ground.
Whatever, if someone is contemplating extending the LWL of their catamaran it is probably prudent to seek advice from the designer (if possible) and the builder.

[clockwork orange]

Laidback,you finally answered the questions that Cat man do was asking, thank you. I had the same thoughts as he did when i read your post and my first thought was that new sails alone always make a big difference.
Steve.

[cchesley]

The one thing hull extensions do that is counterproductive is add wetted surface. I would not expect significant improvement in light airs.

Sounds like adding sailarea/new sails is the ultimate way to essentially 'turbo' one's boat. Add'l horsepower should always work. (within reasonable limits)

I kind of like Bob Oram's "Slim" designs. He essentially starts with bow and stern extensions. Makes sense to me.