Putting a mast and small 3.4 m2 jib on the cabin cruiser

Discussion in 'Sailboats' started by BertKu, Jul 8, 2016.

  1. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi there again,

    I am playing with the idea to put a 4 meter mast on the boat and have a small jib, which I can reeve in and out from the steering position and should I have a problem with the electrics, I would be able to get back to my home base.
    I am getting too old to do some rowing. The local law state that I need 2 oars to have an alternative way of propelling the boat for up to 1 mile at sea.

    Also I am constructing a collapsible keel (Not a folding up or turning in, but collapsible to 2.4 meter long and 12 cm high. You would say, why? the reason is that I don't feel like messing around with the cabin cruiser's hull, other than placing the collapsible keel to the hull. Which could be easy removed. Also I don't feel like modifying the trailer.

    The collapsible keel folds out to 4 x height (or better depth) and should compensate for the mast and jib forces on the boat.

    Are there any real good reason why I should not do the modification?.
    Bert
     
  2. PAR
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    PAR Yacht Designer/Builder

    Well, it all depends on the boat, but a leeboard seems a lot less difficult a thing to arrange and build, then a collapsing device of some sort.
     
  3. BertKu
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    BertKu Senior Member

    Yes, I have thought and investigated leeboards. It does not suit me, as I like to have my CG lowered. Technical, the collapsible is possible and the spring blade pushes it out and the weight of the boat pushes it in, when the boat gets lowered onto the trailer. My CG is then substantial lowered as compensation. Also the special constructed spring blade keeps the extended keel from bending. Like most boats in Holland, the mast will be also collapsible. Bert
     
  4. sigurd
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    sigurd Pompuous Pangolin

    Maybe you want to be able to leave one of the sails up all the time. Lots of small fishing boats have a small rig somewhere on the boat, here in Norway. Usually it is a mizzen though. The fabric is very heavy, like the stuff that you cover trailers with, that doesn't degrade in the sun for many years, and doesn't make noise when pointed into the wind. It's usually blue - fabric with a thick plastic coat - pvc? vinyl? pu? Not sure.
     
  5. BertKu
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Thank you sigurd, appreciate your input, but I am making it as a roll up and can make it as small or as large as I want. I personally think it is much better in my case. Bert
     
    Last edited: Jul 17, 2016
  6. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Here are my problems.
    1) Should I place a permanent keel on my boat, I have to modify my trailer, which I don’t like to do.
    2) If my experimental folding in keel is successful, I am then also able to sail in less deep water.
    3) With a gadget it will be retractable before loading on the trailer.
    This is what I am building for my boat. It is an experiment. I don’t think it is ever done in the world. I think the drawings are self explainable. However if you consider I should make a change or improvement. I am gladly open for comment
     

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  7. sharpii2
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    sharpii2 Senior Member

    This keel design reminds me of patent Center Boards, which were used on some 19th century fishing dories. The problem they had was similar to yours. There simply was no place to retract this thing into. They couldn't used a deep trunk, because the boats had to be stacked. So, what they did was get several strips of iron, drill a common pivot point through one end, stacked them up, then let them splay out like a hand fan. Somehow they connected each strip to the other, so its aft end would only splay so far, instead of them all simply splaying to the end of the pennant. Apparently, this system worked reasonably well.

    IIRC, they did not use springs, but simply let gravity do the work.

    I think the same could be done with your proposed system.

    The only problem I can see is that the individual channels might get cockeyed with one another and jamb either up or down, or somewhere in between.

    It appears that you are trying to make this power cruiser of yours into a motor sailor.

    If this is true, I doubt thirty some square feet of sail is going to do the job.

    First of all, it may be far to little Sail Area (SA) for the amount of displacement you have.

    Second, every bit of Hull and Superstructure above the Water Line acts as SA, except it only helps you down wind. When going upwind, or even across the wind, it contributes nothing but drag.

    To counter act this, you need, you guessed it, more SA. And probably considerably more. Since I have no idea what size this cruiser is, I can not even speculate.

    Another thing to consider is the rudder.

    The rudder on your boat is probably much smaller than one typically on a sailboat of your boat's size. The reasons for this are:

    1.) the boat probably goes faster under power than it would under sail, and
    2.) it depends on prop wash in front of it to give it a good portion of its effectiveness.

    As a sailboat, your boat will probably need a bigger rudder.

    As for the extending keel, it will have to be some percentage of the boats Profile Area plus its SA (about 3-5%). It will also have to be in just the right position, fore and aft.
     
  8. BertKu
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    BertKu Senior Member

    Thank you Sharpii2, useful information you have given me. Yes, that is correct that I am getting too old and one of the rules is to have a second means of propulsion and I don't feel like using the oars. Thus I thought to mount a small jib which I still have from another boat and make this boat a motor sailor. I only need the jib, if I run into problems with my electric propulsion. I am making some room for a larger jib, should 30 square feet (3.4 m2) be too little sail area. I have room for up to 5 m2, but will first play around, with the 3.4 m2 sail area. The cruiser is only 5,5 meter long and displacement with one crew 530 kg. I have photo's placed in the thread under Design. As long I can sail at 1 knot faster than the current or headwind, I am happy. When one is old, time I no longer an issue.

    Thanks for your reply. Bert
     
  9. sharpii2
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    sharpii2 Senior Member

    Ah. Now I'm getting a little bit more of a picture of your boat.

    It's about 18 ft long and displaces about 1160 lbs.

    What I don't know is is it designed as a displacement, semi-displacement, or pure displacement boat. If it is the last, rigging it as a sailboat should be much easier.

    By implying it is electric powered pretty much indicates that it is probably a displacement power boat, which just pushes its way through the water.

    A semi-displacement boat leaves a somewhat longer wake, and one the size of yours might do 8-10 kts.

    A displacement boat the size of yours might do 5-6 kts.

    The 3.4 sm jib actually has about 36.5 sf, which I think is way too little SA for a bout the size and weight of yours. This small jib might enable you to steer a controllable course about 45 degrees into the wind (90 degrees is sailing across the wind). This, as limited as it is, might save you from wrecking.

    The 5.0 sm (53.8 sf), if properly placed might improve your options considerably, maybe to the point of making some upwind progress, but there would have to be a considerable breeze blowing, if you were to fight any current.

    IMHO 7.0 sm would probably turn your boat into a proper motor sailor, in that given a good breeze, she should be able to go where you want her to, without the motor.

    This is, of course, assuming she has proper Lateral Area, proper placement of such Lateral Area, and a sufficiently large rudder.

    If your boat is truly a displacement boat, the rudder may be already sufficient.

    As a general rule, the faster a boat goes (relative to its size) the smaller the rudder has to be.
     
  10. BertKu
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    BertKu Senior Member

    Great information sharpii2, The displacement of the boat is:
    hull 220 kg, extension to the transom 41 kg, + foam 8 kg (still to be added)
    Solar panels 38 kg Metal frames + cabling 26 kg , engine with brackets 40 kg , batteries 98 kg total 471 kg crew 150 kg , additional items 16 kg total 637 kg
    I am planning to bring the weight down. Although I have 40 lithium batteries, the deep discharging SLABS I like to replace with Lithium batteries also. Which would give me a savings of 65 kg. For the savings I like to build the keel of about 35 kg. This also compensate me for the changed CG, which with a mast and sail will move my CG up and by adding the keel, I will bring it down again.

    The hull is certified for 440 buoyance + 160 for the new extensions. Which gives me a near 100% buoyance.
    Yes, you are right the speed will not be more than 5 - 6 knots. I am cruising at 4 knots normally. The length is 16,5 feet. It is a planing hull, but because of the extensions I have placed at the transom, it will be more like a semi displacement boat.
    The sail is only for emergencies. I am quite happy to plot around with only 1 knot more than any current or wind. When I was young, speed was the in thing, but not now I am older. Thanks for your input. Great help to make my mind up in what to do.
    Bert
     
    Last edited: Jul 29, 2016
  11. sigurd
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    sigurd Pompuous Pangolin

    I didn't mean you should copy the rigs, not at all. Just that as long as you have a little sail on a boat, you may want to keep it up all the time when at sea, for damping roll, like the fishing boats. Then a heavy canvas is a plus, because some times the wind is from the bow and those little rigs don't flog like a normal light sail.

    (photo: NTB, stolen from http://nordnorskdebatt.no/article/hvorhen-vi-gar-i-li-fjell)
     

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  12. PAR
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    PAR Yacht Designer/Builder

    The rig Sigurd shows is a riding sail and doesn't propel the boat. It's just as he describes and steadies the boat in roll and keeps her head up on the hook.

    I think he'l need a whole lot more area to do much of anything on that hull. Lots of resistance and area, so consider over 100 sq. ft. as a starting point. A loose footed jib on a mast would do fairly well and could be sheeted in enough to make some windward progress, while being easy to hoist/douse and stow.
     
  13. BertKu
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    BertKu Senior Member

    Hi PAR, did I understood you correctly, that I need at least 9m2 (100sq feet) to get my boat moving. Yes sharpii2 also suggested at least 60sq feet, but better 75sq feet. I will have to make some changes to my plan. slightly higher mast then planned, which makes it heavier and bring the CG higher. Definitely have to throw my heavy batteries out and replace them with lithium. Thanks PAR.
     
  14. sigurd
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    sigurd Pompuous Pangolin

    Even many years ago I believe Li Fe Po became economically competitive with lead acid due to the longer life. The gold standard for hobbyists then was a123 and it may still be. But it seemed to me you already have a prety light boat, and displacement boats aren't all that sensitive to weight for resistance. In bad weather off a lee shore it's more a matter of overcoming the aero drag of the hull. Having enough leeboard/keel area. Having enough sail area. Stability to carry that area.
     

  15. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Sigurd and Par, I made the mast, the folding up brackets, the front folding up beam, and the top of the mast. I am able to get to 7.4 m2 sail jib sail area now, except if I make the sail longer. The height is fixed to 4,2 meter. Total mast length +/- 4.4 meter minus 20 cm for gear. What I don't know, should I make it longer, so that, if I am sailing sort of for the wind, that I can bow it more open and the 4 meter length reef out and could be 5 meter. If the sail is made, I cannot make it larger anymore. Only smaller, with the reefing system I am building. But if I make it 4 meter long, I may feel sorry I hadn't made it longer. What is your advice. I have very little experience in sailing with the jib only. One can always learn. Bert
     
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