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Thread: Hull Extensions

  1. #41

    Default Re: Hull Extensions

    Brad: Performance report of SV Reach's Manta 40 / 42.25 transom extension project. Great photos embedded in their blog post.

    Regards, Mark


    http://www.svreach.com/boat-blog/performance.html

    Length added to sterns: 27 inches

    Weight added per stern: ~ 150 lbs each

    Buoyancy added per stern: ~170 lbs below & 500 lbs above waterline

    Time in boatyard: 5 months

    Downtime due to delays/rain etc: ~5 weeks

    Housemates in & out of shared apartment: 8 couples

    Build cost per stern: ~$3500

    Work clothes ceremonially destroyed: 2 sets "yellow" & "blue"

    Speed increase: ~1 knot motoring & sailing

  2. #42
    Join Date
    Jul 2009
    Location
    currently Columbia/Panama
    Posts
    346

    Default Re: Hull Extensions

    Hey Mark, just saw this. Thanks for posting the links and being interested!

    If anyone has any questions about the build process or performance, I will be glad to answer them.

    Regarding performance - we are easily seeing a 1kt gain all around. This is more speed than can be attributed to the added waterline length (and new bottom paint), so the explanation must be that the bottom step being underwater when we were underway was producing even more drag than I thought. Now, the wake is smooth and even off the stern instead of the previous gurgling, eddying and whirlpools. The new length and buoyancy also significantly decreased hobby-horsing - you can feel the sterns get really stiff when the bow lifts up on a wave and there is no longer any "resonant" movement when the wave passes.

    We are very happy with the extensions. Now if we add 3' to the bows, we would have a 36' boat on 45' hulls. I think that is how catamarans should be built!

    Mark
    Mark Cole
    Manta 40 "Reach"
    www.svreach.com

  3. #43
    Join Date
    Jul 2009
    Location
    'Estrella del Sur' is currently on the hard in Fort Pierce, Florida for hurricane season.
    Posts
    678

    Default Re: Hull Extensions

    Wow, 1 knot is impressive! Thanks for the update!

    Brad

  4. #44
    Join Date
    Oct 2008
    Location
    kefalonia
    Posts
    237

    Default Re: Hull Extensions

    One thing that the stern extensions did throw up was a gradual mis -match of colour from the original hull colour .
    It bugged me more and more over the years and although others said
    " you can hardly see it " , to me it was as if I had stuck two mermaids tails on the back ! nice form but wrong finish ...

    so in April , I whipped Wild Honey out and bit the roller- bullet .
    after 15 years of careful abuse ,

    I painted the hulls !

    a challenge in itself , I used 2 pack PU and with a pal rolled and tipped the outside of each hull , only , no need to paint the inner hulls as the were still as good as the day she was laid up .

    it was a trial in patience , the temp was 22 degrees and mostly sunny
    luckily on the day of the final coat on the " sunny side " it clouded over .
    . not particularly happy with the finish but wet flatted both hulls and managed to get some gloss .
    my arms and shoulders stopped talking to me !

    I pontificated long and hard about painting the boat as it will never be as tough as the gelcoat but I delayed it as long as I could but it was the extensions that drove me to paint in the end .
    the boat is now the same colour , bows to sterns .

    I am glad I did it and should have plucked up the courage sooner

    Gramos
    I didn,t get where I am today by being somewhere else !

  5. #45
    Join Date
    Jul 2009
    Location
    currently Columbia/Panama
    Posts
    346

    Default Re: Hull Extensions

    I got the new gelcoat color matched up with the old really well, so the transition to the new additions are not noticeable at all. This may change over time, of course, because different gelcoats color age at different rates.

    In the near future, the largest "tell" will probably be because the new gelcoat will stay much shinier and "harder" than the older, more porous, gelcoat!

    Did I understand correctly that you wet-sanded a 2-pack LPU?

    Mark
    Mark Cole
    Manta 40 "Reach"
    www.svreach.com

  6. #46
    Join Date
    Oct 2008
    Location
    kefalonia
    Posts
    237

    Default Re: Hull Extensions

    Mark , yes I wet flatted Polyurethane 2 pack , it had to be done as the roll/tip finish looked like the finish on an Austin Allegro from the 70,s
    orange peel !
    I first used 400 then 800 then 12/1500 then went over with medium cutting compound using a low speed "mop"
    I will flat it again next winter I may even paint her again using English paint which has ,when I have used it in the past, flowed better than the product I bought here in Greece . It was good paint but flashed off too fast for a good flow to develop , hence the arm work !
    I didn,t get where I am today by being somewhere else !

  7. #47
    Join Date
    Jul 2009
    Location
    currently Columbia/Panama
    Posts
    346

    Default Re: Hull Extensions

    If you were going to all that wet-sand trouble, gelcoat would have been a better and easier choice! The finish on LPU is ruined by wet-sanding - the high-gloss, hard outer shell is the important part. They make LPU thinners specifically to control flow and flash. Why not spray next time instead? Even if you have to pay someone to do that, it will be worth it.

    If our hull transition begins to change color differently than the rest of the hull, I might consider a graphic in that area that covers the transition. The eye doesn't see mismatched colors when they are separated or have a strong color between them.

    Mark
    Mark Cole
    Manta 40 "Reach"
    www.svreach.com

  8. #48

    Default Re: Hull Extensions

    A much simple extension process that suited my needs. About 2 weeks on the hard and 45 hours of labor.

    Gain a whole knot in speed? That Manta must have been dragging everything. For 2-3 feet of water line you should only expect a few tenths of a knot at most, and in fact that is what I found. What I did get is a much handier area to work, so I am quite satisfied.

    http://sail-delmarva.blogspot.com/20...s-process.html

    http://sail-delmarva.blogspot.com/20...-transoms.html



    "When I was a boy, what was so was so, what was not was not. Now I am a man, things have changed a lot. Some things nearly so, some things nearly not. Is a puzzlement."

    The King of Siam

    http://sail-delmarva.blogspot.com/


  9. #49

    Default Re: Hull Extensions

    Quote Originally Posted by colemj View Post
    If you were going to all that wet-sand trouble, gelcoat would have been a better and easier choice! The finish on LPU is ruined by wet-sanding - the high-gloss, hard outer shell is the important part. They make LPU thinners specifically to control flow and flash. Why not spray next time instead? Even if you have to pay someone to do that, it will be worth it.

    If our hull transition begins to change color differently than the rest of the hull, I might consider a graphic in that area that covers the transition. The eye doesn't see mismatched colors when they are separated or have a strong color between them.

    Mark
    When we did the hull extensions on our Seawind 1000 about 5 years ago we also used LpU paint and also wet sanded. Still looks shiny and new. There was a slight difference in color between the original gelcoat and the LPU so we painted a blue star where they met.

  10. #50
    Join Date
    Jul 2009
    Location
    currently Columbia/Panama
    Posts
    346

    Default Re: Hull Extensions

    OK, I believe you about sanding. My experience is mostly with Awlgrip and I don't think you should sand or buff that paint. Wet sanding cured LPU must be torture. I still think gelcoat is the better, easier way if one is going to sand anyhow.

    As for our speed, yes, I was surprised at the increase and mentioned that it could not be attributed to the added waterline. We are a heavy boat and the previous sterns had their bottom steps immersed when underway. Apparently, this creates more drag than I thought it did.

    Our sole goal when we started the project was to not ever have to "mow the lawn" again. The bottom steps would get covered with grass growth every week and need to be cleaned constantly. I originally was just going to pull out the second to last step over the top of the bottom one and make it even to the existing stern. Then I thought "in for a penny, in for a pound", and decided to do the whole thing so that it looked like it came from the designer and factory that way. I also took the opportunity to redesign the stairs so that they are so much more usable and functional now.

    So we met our goal of getting rid of the lawn, and everything else is just gravy now. The increased performance was a big surprise.

    And I helped fellow short Manta owners - there is currently a Manta 38 using the molds I made to lengthen their boat to 42'!

    Mark
    Mark Cole
    Manta 40 "Reach"
    www.svreach.com

  11. #51
    Join Date
    Apr 2010
    Location
    Mackay,QLD, Australia
    Posts
    353

    Default Re: Hull Extensions

    Quote Originally Posted by colemj View Post
    OK, I believe you about sanding. My experience is mostly with Awlgrip and I don't think you should sand or buff that paint. Wet sanding cured LPU must be torture. I still think gelcoat is the better, easier way if one is going to sand anyhow.

    As for our speed, yes, I was surprised at the increase and mentioned that it could not be attributed to the added waterline. We are a heavy boat and the previous sterns had their bottom steps immersed when underway. Apparently, this creates more drag than I thought it did.
    Our sole goal when we started the project was to not ever have to "mow the lawn" again. The bottom steps would get covered with grass growth every week and need to be cleaned constantly. I originally was just going to pull out the second to last step over the top of the bottom one and make it even to the existing stern. Then I thought "in for a penny, in for a pound", and decided to do the whole thing so that it looked like it came from the designer and factory that way. I also took the opportunity to redesign the stairs so that they are so much more usable and functional now.

    So we met our goal of getting rid of the lawn, and everything else is just gravy now. The increased performance was a big surprise.

    And I helped fellow short Manta owners - there is currently a Manta 38 using the molds I made to lengthen their boat to 42'!

    Mark
    I think it is fairly well established now amongst the multihull designers that keeping the stern out of the water helps drag.

    Loading for a liveaboard at 38-40ft is a real issue well solved by your extension. Good job.

  12. #52
    Join Date
    Jul 2009
    Location
    currently Columbia/Panama
    Posts
    346

    Default Re: Hull Extensions

    Quote Originally Posted by downunder View Post
    I think it is fairly well established now amongst the multihull designers that keeping the stern out of the water helps drag.
    Yeah, they did seem to catch on to that in the past couple of years

    Mark
    Mark Cole
    Manta 40 "Reach"
    www.svreach.com

  13. #53

    Default Re: Hull Extensions

    Lightwave was originally a Richard Woods Gypsy 28 cuddy-cabin catamaran. Lightwave's builder/owners had previously extended the transoms by 4 feet whilst in the Guaymas boatyard; thence sailed home to Vancouver B.C. via Hawaii. Garett and Carllise have recently taken a SawzAll to Lightwave, inserting 5 feet to the centre section of their catamaran. Amazing!

    Here's a YouTube video link to the SawzAll vivisection:

    http://www.youtube.com/watch?v=_0sHe4q613s


    "We cut our boat right in half so we could create a passageway between the hulls. It was a bigger project than we expected (it took 4 months and 1,000 hours), but our boat is now roomier, faster, and nicer looking. So if you ever wanted to know what you could do with a SawzAll reciprocating saw and lots of epoxy, watch this video as it redefines extreme boatbuilding! This video is the "Boat Improvement" version of "Home Improvement". For more catamaran sailing, boatbuilding, and cruising adventure videos and stories, visit Garett and Carllie at: http://www.lightwave99.com " .

  14. #54
    Join Date
    Nov 2008
    Location
    Santa Barbara, Calif.
    Posts
    542

    Default Re: Hull Extensions

    A boy and his Sawzall! These folks are truly after my own heart.

  15. #55

    Default Re: Hull Extensions

    PDQ 39 -- Pacifica -- 3' transom extension YouTube videos posted by the owner / builder.

    Hull extensions Install URL: https://www.youtube.com/watch?v=xEXopT1emSE

    PDQ 36 / 39 Sea Trials URL: https://www.youtube.com/watch?v=g05pyx6nYFo

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