Nesting Dinghy

Discussion in 'Boat Design' started by Kilwinning, Nov 19, 2006.

  1. Kilwinning
    Joined: Nov 2006
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    Location: Gatineau, Québec, Canada

    Kilwinning Kilwinning

    I have had a folding dinghy (Port-a-boat) for the last 10 years. My original objective was to have a dinghy that I could store along my lifelines on my Alberg 30. I expected that it could be deployed from the deck in an emergency. This has proved to be impossible. It would require the Olympic water polo team! I must therefore tow the dinghy. We have found that towing a dinghy can be dangerous in a storm. Try, as we did, to empty a dinghy in a Gulf Stream Storm. Although I have been satisfied with the construction of hull itself the rest is of very poor quality and has required frequent replacements and rebuilds. We use a 4hp which is too much for this dinghy. One big advantage for the hull material is that is impervious to rough landings on rocks or coral. Handy for us since we have a dog that we must bring to shore periodically. We have cruised the Caribbean and our boat's home is the Thousand Islands region of the St-Laurence and Lake Ontario. A lot of rocks there!

    I have been searching for the "perfect dinghy" for some years now. I have finally decided to build my own. I enjoy building things??? I have designed a 10' nesting dinghy which is nearing completion. The finished version should weight less than 120lbs. I am presently completing the mold and will have a completed version early this winter. It is built to be powered by up to a 15hp. and to easily plane. We tested the plug in Lake Ontario this fall and were extremely satisfied by its performance. It is non-sinkable with a double wall fiberglass foam sandwich construction and foam filled seats. This type of construction provides a high strength to weight ratio. It fits nested on the fore deck of our Alberg 30 with ample room to work our windlass and anchors. The nested dinghy could also be fitted, in its nested form, on a power boat's swimming platform or on small davits. The locking mechanisms are very strong and are designed to be able to lock the bow and stern sections together in wavy water in less than a minute. Each of the sections has enough boyancy to support an adult for the locking process. It should meet our need to have an easily deployable emergency dinghy. Both the bow and stern section have sealed water-tight compartments. The stern has adjustable boyant trim tabs. They fold into the stern when not required or when the dinghy is stored. In addition to providing an additional 14" of water-length boyancy they bring the engines center of thrust more forward and allows for the bigger engine possibiliity. They also have knee and foot pad indentations that facilitate climbing into the dinghy from the water. The rub rails are non-marking rubber and give full protection to our boat's hull. The hull will be protected from damage from rocky landings by stainless strips on the plane and tracking fins. Our plan calls for a small dodger over the bow section. A receptical for two piece oars is built into the design of the stern section. The stern will have two small wheels on the tracking fins to help move the nested dinghy over the ground.

    When our dinghy is completed I will have a complete mold available to produce additional dinghies. I don't know how much interest there would be in the boating community for such a design. If there is I might consider putting it into production. All the advice from you or the readers would be appreciated. If additional info. would be of interest let me know and I can provide some rough design specifications and pictures of the work in progress. I have attached a pdf file which contains the rough design and some pictures of the partially constructed dinghy. Our camera is being repaired at the moment so more recent pictures and not yet available.
     

    Attached Files:

  2. Crag Cay
    Joined: May 2006
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    Location: UK

    Crag Cay Senior Member

    I think a lot of cruisers share your enthusiasm for a rigid dinghy that they can get on deck. I also think having a reasonable power capacity is attractive when distances to the 'dinghy dock' and decent fishing grounds seems to get further each year as the number of cruising boats in some anchorages continues to rise.

    However, my first reaction is that you should try to get the weight down. Each part of your boat is still going to be quite heavy to man handle on a foredeck. I think you should aim to have its all up weight under 100lbs, and then work on getting it as low as possible after that.

    Good luck.
     
  3. Kilwinning
    Joined: Nov 2006
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    Location: Gatineau, Québec, Canada

    Kilwinning Kilwinning

    Thanks for your feedback! I am trying to keep the weight down while trying to balance the need for strength and minimize the use of more expensive materials. We will have a better idea in a few weeks??
     
  4. Gilbert
    Joined: Aug 2004
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    Location: Cathlamet, WA

    Gilbert Senior Member

    Perhaps I am not as familiar with today's 15 hp outboard motors as I should be, but won't the motor weigh 75 pounds or more? If so, why would you worry about two hull sections which weigh 60 pounds or so? Mind you I am not saying you should make it heavier than it needs to be but the weight of the motor seems to be a bigger problem. I think the stern could be broader to better support the weight of the motor and person mounting it. However if you have a prototype and all has proven satisfactory you should just ignore my comments. It looks like a very nice piece of work.
     
  5. Kilwinning
    Joined: Nov 2006
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    Location: Gatineau, Québec, Canada

    Kilwinning Kilwinning

    Gilbert,

    Thanks for the feedback. Your point on 60lbs. still being heavy to bring on deck is a good point. I have an Alberg 30 and am planning to design a small block and tackle on my spinnaker pole to help bring it on deck. For a power boat I would flip it up horizontally on the swim platform. As for the engine weight I will have a motor lift on the stern rail. I presently have a 4hp and find it heavy enough to get into my present dinghy.

    The stern was designed to fit comfortably on the bow of the Alberg 30. The Alberg is not a beamy boat and the mast is well forward. I needed to leave enough room at the bow to be able to move easily around the dinghy to my anchors and windless. It is also for hydrodynamic reasons. The dinghy is relatively flat bottomed and it can profit from some additional reserve bouyancy for rougher water. The dinghy is also quite full bodied as it is. When we tested the plug we used a 9.9hp. Although, we didn't weight it, I expect it was at least 60lbs. It didn't pose any weight problem with my additional 170lbs. at the stern. I don't think that 75+lbs will make much difference. When we tested the plug we only had plywood planing fins on door hinges. When the dinghy is completed it will have planing fins that are buoyant, which when deployed, will provide an additional 14" of waterline buoyancy.

    In normal conditions I probably won't store the dinghy always on the deck. I will probably tow it from the stern. I only becomes very important to me to have it on deck when we make longer open water trips and expect rough going or I want to sail a bit faster. I will also try and see if it can be towed, with the front section stowed in the stern, attached up from from the rear deck like some tow their inflatables. I don't know if this will work or not???

    I hope this explains some of my design reasoning?? Thanks again for your feedback!

    Kilwinning #446
     
  6. Kilwinning
    Joined: Nov 2006
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    Location: Gatineau, Québec, Canada

    Kilwinning Kilwinning

    Gilbert,

    I had a look at your profile and I saw your kyaks. They are really very nice!

    Kilwinning
     

  7. barnaclephill
    Joined: Jun 2007
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    Location: melbourne, australia

    barnaclephill New Member

    Nice nesting dinghy. Very substantial, but my thought is that it will be heavy to put on the deck each time.

    Here's what I have done. I built a 9 foot nesting dinghy the simplicity9N from www.Bandbyachtdesigns.com but instead of the wide transom, I made another front half, so it would fit on the foredeck as a canoe-stern vessel. However, I stretched the widest part of the boat by 8 inches and then cut off 8 inches at the rear, to allow space for the rudder/outboard. Here's a pic nested on deck before painting:
     

    Attached Files:

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