efficient 10m displacement powercat (build thread)

Discussion in 'Boatbuilding' started by groper, Apr 15, 2012.

  1. Ad Hoc
    Joined: Oct 2008
    Posts: 6,974
    Likes: 919, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    That's what it is all about. Longevity.

    In NA terms, we call this..fit-for-purpose. Sadly not every boat is designed and built as such.
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,030
    Likes: 918, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Does the boat have foam buoyancy, Groper ?
  3. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    No... there is sealed buoyancy compartments... typical of most modern sailing cat designs these days...

    And If every compartment became flooded - i still dont think the boat can completely sink - i worked out the volume of foam in all of the structural foam core panels was something like 4 cubic meters... so there is enough buoyancy just in the structure itself to keep her off the bottom :)
  4. Richard Woods
    Joined: Jun 2006
    Posts: 2,208
    Likes: 166, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    I have found that you need to anchor from the centre and use a bridle on multihulls over about 9m. Smaller ones are OK to anchor from a bow.

    If it is windy and gusty we often leave the outboards down to act as "weathercocks"

    I hadn't realised you had such a small tidal range

    Power cats are lighter than sailing cats. No boards/keels, rudders, mast strengthening. Also the torsional loads are less without the rig twisting everything

    Here is a photo of a Moorings 39 power cat and sailing cat. As you can see they are identical, same hull (at least above the WL) same windows, cabin roof etc. Of course that is no problem with a charter boat, because charterers don't care how good the boat is, they just want a"floatel" and it saves the boatyard a lot of mould costs.

    But a proper sailing boat needs a different cockpit layout, a mast beam in a set position etc so it seems illogical to have a power cat with the same deck layout as a sailing cat.

    I get lots of people come up to our Skoota to ask "is it a sailing boat?" I point to the nearest powerboat and say "is that a modified sailing boat?"

    Richard Woods of Woods Designs


    Attached Files:

  5. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    you dont mean like this do you Richard? :D


    or perhaps this, :D

    biplane rig2.JPG

    If i decided to do this one day, i would extend the transoms another meter aft and cut away the bottom of the hull to provide the buttocks a run upto the new shallow transom futher aft... and ofcourse much smaller engines to go with the changes...

    I made the main beam located for the bermudan rig strong enough to take mast compression loads also - all the laminate is already in there, it s giant I beam with lots of UNI along the top and bottom...

    the biplane rig might also be another option, i also made the next beam bulkhead further forward extremely strong also for this purpose, and same again for the rear beam to take a sheet track for a boom etc...

    I remember you saying at one point that you bet the boat will be very stiff - well your right, she is a very stiff cat - you cant feel any twisting of any sort in a seaway or if someone jumps up and down on the transom or bows etc like you can on some of the more flexible designs out there... i know ive been on a few cats where you can really feel the movement and flex as they pound in a quartering sea... this boat just doesnt move at all...
  6. Openwaterguy
    Joined: Apr 2016
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Pacific Northwest

    Openwaterguy New Member

    Groper, have watched your project with great interest and for awhile. I have a similar project going and would be keen to compare some notes. I've gone with 60s and get 19knts. I would put up a picture but can't get it sorted on my phone. Happy to email you one.
  7. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Your profile wont allow me to send you a private message - if you change your settings i can give you my email via private message. Otherwise - i cant publish it here or the spam bots will grab it and forvever bombard me with junk from this day forward :D
  8. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Finished off a few little details on the front deck etc... we beached the boat and put in a couple of through hulls for the watermaker the other day and decided to take a pic. Dive compressor is located under the white cover beside the hatch. Would have been nice to have it on the back deck but it does get in the way back there too, plus with it up here and the 4 scuba tanks in the locker directly forward of it ive managed to get the boat CoG right and its sitting about dead level now. Water maker is also up forward for this reason also. Ill get a few pics of our DIY watermaker when the last few details are plumbed in...


    Next, i really need to get started on this fore beam and trampoline... time is running out before our overseas trip which is departing in 4 weeks :eek:
    God damn gubment thieves now want $1550 for national ship registration so we can leave australian waters! :mad:
  9. jorgepease
    Joined: Feb 2012
    Posts: 1,620
    Likes: 49, Points: 48, Legacy Rep: 75
    Location: Florida

    jorgepease Senior Member

    Amazing boat Groper!
  10. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Well the DIY watermaker seems to be a success, works better than i expected :) Both Mick from ROAM and I have both got our systems up and running as per the design weve hashed out on here. Dave still needs to get his boat in the water to test his! :p

    Im getting 72 litres per hour with the VSD running at 34hz and water temp of 27degrees @ 800psi. It can be ramped upto 60hz if we want and the total flow rate through the CAT pump is almost doubled from ~3L per minute upto ~6litres per minute. The product water flow will not double, only the total flow, so the recovery rate is not as favourable but it will increase somewhat - how much we dont know yet. Running at this speed (34hz) uses 50amps @ 12V. Of course we can slow it down aswell, probably down to around 20-25hz for an optimal energy efficiency standpoint. How much power this uses i also dont know yet, but it should be proportional to the flow, so 1/3 slower should use 1/3 less energy, or around 34 amps give or take.

    a few pics -


    Tucked it into the forward closet area...

    The VSD and line reactor which drives the little 0.75kW 3phase motor/ CATpump.
  11. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    I have put the specs of the watermaker down here for those interested as I've had a few people ask me about it now... anything else you want to know I'll add it in here as it comes...

    Pump is a Cat pump 2sf15seel , 1.5gpm @ 1725rpm.
    Motor is a 0.75kw 3 phase induction motor, general industrial type, 4 pole 1400rpm @ 50hz
    VARIABLE SPEED DRIVE- 0.75KW single phase input , 3 phase output. 15uH line reactor for filter.
    Membrane is a dow filmtec sw2540, single stage.
    Lift pump is magnetic drive (no shaft seal) 12v BLDC pump, 4amp max.
    Sediment filters 20 and 5 micron with combined carbon / sediment elements.

    That's about it. Works better than I expected and it's pretty quiet too :)

    For small scale systems you coukd probably go down to the smaller pump like the 2sf10seel and it would be a bit more efficient again.

    Last edited: May 5, 2016
  12. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Ive started to make the forebeam to take the trampolines and catwalk. This will make it easier to handle the anchor and also provide a place to relax, its nice being up the front away from the engine noise so this is something ive been wanting to do for a while now.

    I also plan to incorporate a retractable ladder which stows under the catwalk so we can walk down off the front onto the beach and get back on board without getting wet etc. This also means we dont really need a tender as the boat only draws 400mm from midships aft...

    The foam was hot wire cut by a local guy. Im simply going to wrap it with 2000gsm of uni glass and 1200gsm dbias... Apply all the infusion consumables, bag it, and then slighly bend the whole thing using gravity as my apprentice. Once its in the bend im looking for, ill let the resin flow and it should infuse a lovely cambered beam in 1 shot. Once thats done ill fit it upto the boat and glass over the ends.

    Once the beam is filled and painted, ill grind some paint off the boat, offer it up and glue it in place... thats the plan anyway :D


  13. DGreenwood
    Joined: Aug 2004
    Posts: 722
    Likes: 40, Points: 28, Legacy Rep: 507
    Location: New York

    DGreenwood Senior Member

    wow...all very nicely done Groper. I'm particularly impressed with your systems install. Nice job on the water maker. Doing a well thought out job on systems makes life so much easier later on when it comes time to actually use and maintain this stuff.
  14. Speedling
    Joined: May 2016
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Cedar Lake

    Speedling Junior Member

    Absolutely beautiful boat!

    Now, this is more of a displacement hull, but you are reaching over 20 kts? impressive!

    I wonder if it was a bit more of a planing hull with some more power, what would it do?

    What's the range on this thing?
    Following closely and dreaming of building similar!

  15. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Still adding bits pieces as time goes by, seems the work never ends... peice by piece the boat gets more and more finished... a few more pics to follow soon...

    We are, at last, in the final days of packing for a trip in the boat i designed and built, destined for another country... we are taking her upto Papua New Guinea for a 6 week adventure across the Louisiade archipelago...

    Our range depends on the speed of course... on the 600 Litres of fuel we carry in our built in tanks, we can make about 1000 nautical miles at 8 knots. If we increase to 18 knots, then our range is only about 400 nautical miles... for big crossings, fast speeds are a little opulent :)

    If it were a planing hull - i dont think it would be tremendously different from an efficiency or speed viewpoint, only the different seakeeping characteristic would be worth noting id say... I could have made it far more efficient at 8 knots without the deep transom, but higher speed efficiency and achieving correct CoG would have been difficult without long rear projections from the hulls... - landing fish caught on the troll without snagging them up in the outboards is another problem if going that way...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.