My catamaran conversion project

Discussion in 'Multihulls' started by massnspace, Jan 31, 2015.

  1. massnspace
    Joined: Jan 2015
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Seattle

    massnspace Junior Member

    36' Macgregor sail to power catamaran conversion

    Hello fellow designers, builders and dreamers.

    I am currently converting a 36 Macgregor sailing cat to power for a business I will be starting this summer. I have a blog that details this process, and invite anyone interested to have a looksee. Here is the address:

    If you have any comments and/or questions, I would be interested to hear from you…especially if you have actual experience in design and/or construction using foam/epoxy, or have attempted a similar project.

    I am very busy building this boat, so will only be on this forum about once a week.

    Happy multihulling!
    Last edited: Jan 31, 2015
  2. SleepyOldDog
    Joined: Apr 2012
    Posts: 9
    Likes: 1, Points: 0, Legacy Rep: 19
    Location: Virginia

    SleepyOldDog Junior Member

    Does your design need to be certified by the USCG for commercial service?

    I read your complete blog. Interesting project!

    While my direct professional experience is not in fiberglass/epoxy I was in the marine industry for 25 years - big steel stuff mostly.

    I did not see mention about how you intended to have your design/boat "certified". If you are going to operate a commercial business you will need some form of liability insurance. Insurance companies generally have some requirement for a boat survey and/or manufacturers certificate of compliance with all applicable Federal Laws/Regulations.

    With the extensive refit you are doing, I think the USCG, your Insurance Company and the state of Washington will consider you the boats Manufacturer. So you will probably need to be able to respond to all the Federal Regulations and insurance requirements in order to get a business license. Regulations/Rules are too many to list...

    Some starting references: (You must purchase the actual documents.)

    As you probably know, you have a very skilled multihull designer/builder in your area. He has designed many catamarans for charter service. Over the years, he has written in his blog about the design analysis and calculations required by the Coast Guard. He would be the first person I would contact if I was undertaking a project like this. He should be able to tell you what type - if any? - USCG certification and manufacturers documentation may be required. (He is a busy professional and you are undertaking a professional/commercial enterprise so you should expect to pay for services.)

    Maybe, based on carrying fewer than, say, XX passengers you do not need to comply with some or all of the regulations? This is not my area of expertise. But, I think it would help to get all these questions answered as early in the project as possible.

    Best of luck with your new enterprise.
  3. John Perry
    Joined: Nov 2003
    Posts: 280
    Likes: 30, Points: 28, Legacy Rep: 129
    Location: UK

    John Perry Senior Member

    Hi, I read the most recent post of your blog and one detail of your work puzzled me, that being the longitudnal slits cut in the bottom of the hull just forward from the transom and the raising of the part of the hull bottom between these slits.

    You say that you plan to add weight to the boat beyond the orginal design intention and that ' If I do nothing, the rear of the boat will tend to drag down and not let the water exit off smoothly'. Surely forming a 'groove' in the aft bottom of the hull will remove what was originally underwater hull volume, causing the aft end of the boat to sink deeper. Also it means that the flow of water leaving from under the transom will have more of an upwards velocity component, again causing the stern to 'drag down'. The slits look fairly short and close together, so the actual effect may well be next to nothing anyway, but I would have thought that if you want to keep the stern up at speed you should push the hull skin between the slits down, not up.

  4. massnspace
    Joined: Jan 2015
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Seattle

    massnspace Junior Member


    Clarifications on the design and intent, based on the 2 replies:

    1. The boat will be used for a 6-pack charter operation….no coast guard inspection is required for these types of boats.

    2. The slits in the stern are to raise the waterline slightly there…without doing that, there may be quite a bit of "dirty water" trying to exit off the back…the idea is to raise it up a bit as to let the water cleanly exit off the rear at speed. I will also be lengthening the hull a foot or 2, so will increase waterline length and load-carrying ability, as well as reshaping the very rear to be a flatter section, to give a bit more lift.
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.