Design Suggestions

Discussion in 'Boat Design' started by messman, Nov 21, 2008.

  1. messman
    Joined: Nov 2008
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    messman Junior Member

    Ok here is where all of you experienced types get to tell me that I am a fool and what not, but even more important get to give me your suggestions of boat designs that you would suggest. Now please keep in mind I believe in jumping in the deep end or I dont jump in. So here goes.

    I am thinking about building a 27' Dory design with a cabin superstructure.

    I will be using this craft in mostly bay type areas around the Gulf of Mexico, with limited open water use. It will be used for family outings, fishing, and when the son becomes dive certified, as a diving platform.

    Do you all think this would be a good design? or is there another design you would suggest?

    Chris
     
  2. Boatpride
    Joined: Oct 2008
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    Boatpride Boatpride

    Dory Article For You

    Hi Messman,

    reading through your post i got curious about the design so i went hunting and

    found an interesting article which should erase any doubts you have about

    building your dory. http://ezinearticles.com/?Choosing-

    the-Best-Easy-to-Build-Small-Boat-Design&id=951274

    You'll see the dory reference after a few paragraphs. There are several

    styles of Dory mentioned and the author of the article is credible.

    Hope your son flourishes with his dive certificate.

    :)
     
  3. messman
    Joined: Nov 2008
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    messman Junior Member

    Boatpride,

    Thank you so much for the response. I am glad to see that the choice, in someone elses eyes, appears to be a good one.

    The individual who wrote that article, Mr. Spira, seems to be a very nice man willing to help out. I have e-mailed him a couple of times to which he responded quickly. I just wanted to make sure the design I am thinking about is a good choice. You have also calmed some concerns of mine by saying he (Spira) is credible. I have not had the opportunity to research him yet.

    I am still very much interested in seeing what design opinions others have, what others recommend I should build.

    Chris
     
  4. Tad
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    Tad Boat Designer

    Umm....Mr. Spira is credible because he suggests novice builders should build dories....oh and he also sells dory plans...what luck! :D

    Seriously, of course Spria believes in the boats that he has designed. Obviously he cares about the type (dories) and it's use. Dories have their place I'm sure, mainly in the hands of experienced people who need to carry heavy loads in open water. Generally dories have narrow bottoms in comparison to more conventional (modern) vee or multi-chine forms. This means the dory is initially tippy, until the boat has say a ton or so of fish aboard. A tippy boat tends to scare novices...this is not good for family harmony.

    MessM you mention a 27' dory, I assume you're thinking of a St. Pierre fishing dory? If so this is a really poor choice for a boat with cabin, they were never intended for this. Again the narrow bottom in combination with high sides and higher cabin makes for a tender (tippy) boat. Something with a typical vee bottom and lower sides will be much better for family use, especially getting a diver on and off.

    Also Mr. Spria could improve the safety of his designs tremendously by including a splash well inboard of his transom cutouts. It's very easy for a small wave to come through that low cutout and swamp the boat.
     
  5. rasorinc
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    rasorinc Senior Member

    Dory

    Here is a dory plan with the outboard forward of the transom. you can get an idea of how strong it is built. Stan
    https://www.boatdesigns.com/products.asp?dept=277 PS they have cabin layouts for it also

    If I had young ones with me out in salt water and getting in and out with diving equip. I would consider a Cat. Here is a link to one that also can have a cabin. There are ones that are trailerable being 8'-6+ wide. Stability is everything with young or old aboard, Just more info for you to consider. https://www.boatdesigns.com/products.asp?dept=781
     
  6. tom28571
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    tom28571 Senior Member

    Tad,

    While I agree with your arguments, I suspect that you may be pissing against the tide. "Dory" is a word that has reached almost cult status in the novice boating world. There are a couple that have a credible reputation, like the Simmons Skiff of my area that work well for the task that Mr. Simmons set for them. That is, fishing the inshore, inlets and near land ocean waters of the Carolina coast. Kilburn Adams seems to have a workable solution with his Skiff America, which has, as you advise very little cabin structure. The C Dory from your part of the country is very successful is selling all their production although it has some undesirable quirks like you mentioned.

    Warning someone off a dory for a cruising powerboat or a sailboat is a little like trying to change their religion. That sweeping sheerline must be a narcotic.

    Some, like Renn Tolman have widened the bottom to the point that is is no longer such a tippy dory and have made a well received boat out of it. The older Simmons is also a bit like that and has the open transom well.

    Another magic term to go with dory is the double ender although George Calkin has made a great boat for running inlets with one. He does add aft wings under the water to give it a reasonable planing performance though.

    In other words, it's possible to make good boats for particular purposes from designs that are not nearly as good for general use as most novices think. So, I agree with your attempt to make messman think seriously about the problems of the dory before jumping into a building program.
     
  7. messman
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    messman Junior Member

    I am very open ideas here, and I am not stuck to one design. I do like the design concept of the Cat. and want further options. The Dory design that was presented by rasorinc is very similar to the Dory design I am looking at from Spira, the one problem is that with it's 9' 8" beam it's not trailable, major draw back there. Here is the dory design I am concidering, which is based on the Pasific dory designs. http://www.spirainternational.com/study/SitkaStudy.pdf
    It seems to have the wider bottom that Tom has pointed out in his post. I guess I should have provided the link with the initial posting, sorry.

    Please more discussion on this issue, I truly want the input from you all. This will allow me to make an informed decision rather that jumping into the deep end of the pool only to find that it was filled with jagged rocks.

    Chris
     
  8. rasorinc
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    rasorinc Senior Member

    new boat build

    here is a trailable dory and cat. How many people will you have in the boat? If you want to do motor sports the Dory is not the boat to do it in. The Cat gives you much greater flexibity in usage. Stan


    https://www.boatdesigns.com/products.asp?dept=900https:

    https://www.boatdesigns.com/products.asp?dept=372
    If you go to the Glen L site, go to customer photos you click on Wildcat and you will see a complete building job. Click on V dory and you will see various builds. Just more info for you. Hope it helps
     
  9. messman
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    messman Junior Member

    Thanks Rasorinc, I will take a look at these.

    Chris
     
  10. tom28571
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    tom28571 Senior Member

    I thought I would throw in some numbers that may help see the difference in different "dory type" boats and lead to better understanding of the types. If the crew stays inside the beam of the hull bottom, most any boat can be considered stable. In a very narrow bottom dory like Bolger's Light Dory, you need to sit in the center with your hair parted in the middle.

    A good indicator of tenderness is probably the hull bottom beam to sheer beam ratio. Some numbers for a few boats are:

    Bolger Light Dory ~ 0.5
    Glen L Big Hunk = 0.62
    Gerr Offshore Skiff = 0.62
    Spira Pacific Dory = 0.67
    C Dory = 0.71
    Simmons Skiff (typ) = 0.71
    Tolman std = 0.71
    wide body = 0.73
    Jumbo = 0.75

    Typical non dory ~ 0.80
    Bolger box = 1.0

    Moving from top to bottom on this list gets you from very low to very high initial stability. It does not show that any of these boats are safer in all conditions than any others so one with even very low initial stability may stiffen up more or less than others when heeled. Comfort, especially in cruising, is often closely dependent on initial stability though. A fishing boat can, in my view, accept much lower initial stability than a cruising boat, especially as there will always be some high up structure that makes stability worse than the number might indicate.

    I would think that the Simmons and Tolman Standard are fine for a fishing boat but barely marginal for cruising. I'd place the C Dory a bit low on that scale while realizing that there are scads of owners ready to skewer me for that opinion. I and some of them, if they admit it, have had a C Dory become very stable on its steeply flared side after a roll going downwind. Not what I call comfortable.

    I'd like at least 0.75 of the Tolman Jumbo and preferably nearer to 0.80 in the range of Devlin's small cruisers. Bolgers boxes rate so high here because their sides are vertical and it is not possible for the crew to be outside the bottom beam. I would have no qualms about going offshore in Gerr's 28' Offshore Skiff but would not care to take a cruise in one. Stepping aboard one at the dock is a surprise and you should warn anyone aboard when you do that. It banks waaay over in a turn and I expect other small boats with a similar ratio to do likewise. The one I drove was owned by an airplane pilot so he probably did not mind too much.

    These are my personal thoughts and I would like Tad's or others views here.
     
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  11. messman
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    messman Junior Member

    Tom,

    That is verying interesting information. How do you come up with the number, or in other words what formula do you use to come up with the number.

    Chris
     
  12. ancient kayaker
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    ancient kayaker aka Terry Haines

    You can have too much of a good thing when it comes to primary stability, especially if you are caught between wind and water and a crew member has a sensitive stomach. It's the secondary stability that actually saves your butt in a blow.
     
  13. PAR
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    PAR Yacht Designer/Builder

    What Tom wisely points out is that one; there are many different types of dories, two the type has evolved considerably, incorporating many variants all called (many not rightly so) dory and lastly, that modern renditions of the dory are considerably different then the real dories that were fished extensively in the 19th century.

    The 19th century dories, for the most part (all 15 or so variants) were heavily built by modern standards, though considered light in their day. They were also intended to "load down" uniformly, without ill handling or bad manners while bringing home a ton or so of fresh fish. These types, when lightly loaded are considered quite tender by today's standards, though an acceptable trade off then. These "antique" craft, should be left to those interested in preserving the type, because as sailors or pulling craft, they suck frankly.

    Enter the modern dory or what is often referred to a semi-dory or modified dory. These are more skiff like in appearance, having less flare in the topsides, less height in the aft portions of sheer and most importantly a wider bottom beam to improve initial stability. Other features will include considerably wider transoms, compared to the tombstones typical of the antiques or the fat buttocked double enders. These "improvements" are a natural progression of the type and for the most part have changed them into a different breed.

    If a modern semi dory (power version) or modified dory (sail) hull form is selected, for a designer familiar with the type, then you'll do well with your planned excursion/dive boat. If you elect to "doctor" up a conventional dory or a hull form that isn't well suited to your intentions, you may well end up with a boat that you just don't like to be out on.

    Personally, I wouldn't select a dory for a dive platform. For this you want a boat capable of moderate deep water work, but a reasonably stable hull form. A dory, modified or not, isn't well suited for this. Weight needs to be kept very low in a dory, so out goes the cabin idea.

    If working in the coastal gulf and other Florida waters, you'll want shoal draft, to go along with this stable platform. This means a much wider beam/length ratio then typically found in dories of any type. I'd recommend a Sea Sled design for ultimate stability, extreme shoal draft and lots of deck space for a house. If this shape frightens you, then a moderate V hull, with 16 degrees or less of deadrise. This will handle the occasional trips off shore, while still providing stability.

    There are a lot of questions yet decided about your needs, much of which will help determine the hull form you need, such as the desired general speed, power train, percentage of time parked over a diver, compared to exploring the coastline, accommodations, equipment, budget, etc.
     
  14. tom28571
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    tom28571 Senior Member

    Paul,

    That adds a lot of flesh to what I was saying. I hesitate to say too much about the dory as a type, because there have been so many changes and some people have a fixation on them. In general, I think there are better boats for almost any use than dories which have been modified in an attempt to meet such requirements. Any use needing work to be done over the side, like diving for instance, will suffer from very much flare, which is the main feature of a dory.

    Messman,

    It's not much of a formula, just a measure of the flare of the hull sides. Just divide the max hull bottom beam by the max sheer beam. Higher numbers represent higher initial stability and vice versa. Smaller boats are more affected by the result because loads like crew weight, gear placement and any superstructure like a cabin have relatively more effect on stability in small boats than in large ones. Larger dories are also more likely to have some ballast.
     

  15. ancient kayaker
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    ancient kayaker aka Terry Haines

    The usefulness of the true dory is long past, it's kept alive by enthusiasts with a historical, not a practical perspective. In its day its advantage was it could be built cheaply by nearly unskilled labor and, if you got a few important dimensions right, it would work as expected, even if your workmanship was a bit off. Also, if you got caught out in a bad blow far from shore or the mothership you can lie down in the bottom of your dory with a good chance of corking it out alive, and a dory can haul a heck of a load. Dories carried on a ship for fishing etc were made with removeable thwarts and seats so they could be stacked on deck.

    I based my first two boats on the dory concept for its simplicity and ease of design. Pretty to look at, but awful things to use; suffice it to say, my designs have moved on.

    I think there are better places to start for almost any boat unless your requirements correspond with the needs of its inventors. Now I have to head down to the bomb shelter ...
     
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