Request your input on my design

Discussion in 'Boat Design' started by richardf, Jul 15, 2013.

  1. richardf
    Joined: May 2013
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    Location: Michigan

    richardf Junior Member

    I am less than 2 months from my move to Jacksonville, FL and a house which is 7 minutes from the ICW on Beach Blvd. I have a good fishing skiff (I built a Spira Seneca). The wife wants an ICW cruiser that we can overnight on. I told her the minimum size is 24 foot, and we can't afford the gas to push a 24 foot planing boat around. We have to go with low HP displacement speed. She is okay with that. Here is the hull form I came up with:

    My thoughts are:
    I like wooden boats.
    24 foot overall length (most I feel I can afford to build and have space to build).
    Simple plywood on frames construction (Spira methods).
    Outboard power (two 9.9's for reliability, or one 25).
    3:1 beam to length for efficiency at displacement speed.
    No flare to maximize internal space (need to sleep, cook, and poti)
    Room for two day-guests.

    I am requesting comments on hydrodynamics only and ICW seaworthiness only. I realize topsides and construction methods are another matter, and I will request your input later after the hull shape is set.

  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I have a 26' riverboat that is much like Egress (below).


    Of course it's two feet shorter and it has an elliptical stern, rather than the transom shown on Egress. It's a displacement cruiser, currently setup for outboard, but an electric hybrid is in the works with a straight shaft. Contact me by email (click on my icon) and ask about "Chiusa" (attached).

    As to your other concerns, it does have flare, which helps keep the boat dry as well as serves other functions, like reserve buoyancy and plunge protection. It's beam/length ratio is significantly over your 3:1 requirement (it's 3.68) and she's shaped to be efficient at displacement speeds (Cp .56). Currently she can handle a 10 - 30 HP, with the 10 being fine, though you'll lack reserve capacity for contrary winds, opposing currents and chop. A 15 or 20 HP are the best arrangements, with a 30 HP for those that want to push her a little past her theoretical hull speed. Twin 10's would offer a level of redundancy and a noticeable maneuverability advantage.

    I wouldn't recommend building this boat as the Spira Seneca's dories are done (though she could be). The dories he modeled that after, need some heft, to make them "settle down" underway, which is typical of dories. In a boat of this size (24' - 26'), you'll just be way heavier than necessary, which is material you have to pay for and ask your engine to drag along, unnecessarily eating into efficiency and load capacity. As designed, she's a bit of hybrid between plywood over ring frames and a true taped seam build. This saves a lot of weight (maybe 30% - 40%) over a conventional plywood over frame build, reduces the number of "boat parts" by ~50%, not to mention the money and build time, spent on the decreased material requirements.

    The hull form is flat bottom, but is also available in a warped V bottom. The outboard is is a well, but could be transom mounted. There are several variants, sheer treatments, etc. She'd be easily trailered and well suited for your needs.

    Attached Files:

  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Richard, not meaning to be a smart-rse, but your boat wins the Fugly Award hands down, even though the drawing does not define the lines. :D Why worry your head designing a boat when you can browse through any amount of established designs to purchase at reasonable cost, you really want something that is easy to build that will cope with the conditions you use it in. Is 24 feet some kind of statutory minimum, or just a length you settled on ?
  4. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Richard, you design as drawn (assuming the horizontal line is the chine) can't be built from large sheets of plywood. The shape of the bow would need some form of cold molding or similar which complicates construction. The sweep up at the stern is too abrupt and the drag will not be much better than not sweeping up. Also you need to estimate the weight of the boat with fuel, etc and you and your wife and then find the height of the waterline with the corresponding displacement. Unless the chines are submerged or close to being submerged the boat may feel "tippy".

    Also consider Tom Lathrop's Bluejacket designs. While they are designed to plane the hull shape is also pretty efficient at slower speeds, better than what you've drawn. They are economical over a wide range of speeds. While Tom suggests a 50 HP outboard for the 24 there is nothing which says you can't put a 20 HP engine on one and just accept a lower top speed. But keep in mind that 50 HP 4 stroke outboard will use about the same amount of fuel as a 20 HP 4 stroke outboard at the 5 to 6 knots, and the larger engine provides the option of running faster if a storm comes up or you need to get home. The Bluejackets have a lot of room inside. If the 24 doesn't have enough room inside he has several longer versions. The berths are large enough to be comfortable for larger adults which is not always true. The construction process is relatively simple and well documented. The fishing skiff is good experience for building a Bluejacket.
    Last edited: Jul 16, 2013
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Agreed in the "lines" provided, just way too many common novice errors to consider. No offense intended Richard, it's just not a viable design for several reasons.
  6. nzboy
    Joined: Apr 2011
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    nzboy Senior Member

    It looks like a barge

    Paul if you have time can you give 10 points why Richards boat is a barge! I think the stern is not a developable shape .Richard I think you need to know most designers just rip off someone elses shape .The easiest way to do that for example is spend $226 and buy a plan of glen l (Hercules ) put a Rangertug top on it .If you strip planked it, you then can say it is" my own design". Most of us who dream of boat designing just spend countless hours studying other peoples designs. The over riding concern it must be beautiful to behold
  7. dskira

    dskira Previous Member

    In your eyes and opinion you should have added. Generalities from one person is not a norm per se. It is just an opinion, and not a very knowledgeable opinion.
    Stealing a design as you propose to Richard show a poor morality and lake of understanding of honesty. You should consider trying golf. It will be less dangerous for everyone.
  8. hambamble
    Joined: Jul 2012
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    Location: Gold Coast, Australia

    hambamble Junior Member

    Always think about the budget: If you want to OWN a boat, the cheapest and fastest way is to go and buy one... If you want to BUILD a boat, it will almost always cost more than buying. As you are investing so much, I always like to think that resale value is important. You will never get back what you spend building it, and pretty boats sell faster and for more... In my experience, plywood boats will sell for less than planked hulls. On this type of boat, chines will sell for less than round bilge. I appreciate that a round bilge is generally slower and more complicated to build (therefore normally more expensive), but its worth considering when you go to sell.

    I like the twin engine concept for reliability, but would suggest that a good quality 25 may be better, with perhaps a stern mountable 5 hp to get you home in an emergency - you could always use it on a tender to justify buying the two engines. A larger engine can come with perks like electric start, and you can usually fit an alternator for running on board electrics (you can fit alternators to some of the 10's too, but I don't think all).

    I will say this about seaworthiness... Its not a simple question. It depends primarily on displacement, and the location of the center of gravity. The basics are as follows though:
    Round bilge designs are more efficient in displacement mode than chined hulls.
    Chines are better if you want to get up on the plane (at a guess, 25 hp, with this sort of design won't cut it).
    I always tend to find round bilge boats more comfortable at sea.
    The lower down the center of gravity, the more stable the boat is... so keep heavy things like engines, tanks, anchor chain etc. as low as possible.

    The other suggestion I would have give is that if you want an overnight boat, perhaps consider converting an old timber fishing boat. It would be a fun project. You can usually get one quite cheaply, with a reliable diesel engine. Do the traditional layout of a V birth upfront, and a small galley in the doghouse. Can probably fit a head just aft of the birth.

    My other suggestion is to consider where you can get in a day from where you intend to keep the boat. If your cruising speed is 6 knots, in 10 hours you could go 60 miles, if cruising speed is 12 knots, in 10 hours you could go 120 miles.... that effectively gives you 4 times the area to cruise on overnight trips. Get a chart or two and see whats nearby. It just might be that an extra knot or two of speed gives you access to different ports or islands and its really worth the extra money.
  9. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Richard, the other guys have advised you wisely. Ignore the comments from NZBoy and consider the other replies. The boat that Par has shown would fill the bill nicely, easy build, good efficiency, and it looks pretty sharp too. But there are many other good designs out there.

    When you choose one do give some consideration to shallow draft. If you are going to mess around in .the iCW or go gunkholing you will not want a deep draft boat. From Jacksonville you can explore the Saint Johns river all the way south to Sanford and Lake Monroe. That'll keep you occupied for a long time. There are some beautiful scenes along that inland route restaurants and marinas with gas docks every now and then, The river is nice fresh water too.

    Matter of fact, if the boat is not too big you could manage to cruise inland all the way to Eustis, Tavares, and Mount Dora.
    1 person likes this.
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Light draft on Egress is 10.5", light draft on Chiusa (the attached file) is 7.5". Yep, I've made the cruise Messabout is mentioning, down the St. John's to Lake Monroe. There's no direct connection to the St. Johns any more. The lock that once supported this passage has been in disrepair for years and the Army Corp refuses to make the necessary expenditures. The St. Johns is shallow in places, but if you stay in the channel, you can come down with a lot of draft. I brought a 48" draft powerboat down to Lake Monroe some years ago, during the last dry spell, with no issues. There was a time when you could come all the way to lake Eustis, but not any more, except by canoe.

    As to what NZboy (his handle is a tell I think) is talking about, who knows, but just because my boats have the pointy end facing forward (seems to be a fad in boats lately), doesn't mean it's a copy of anything. Hell, I wish it was, so I wouldn't have had to put the hundreds of hours of effort into their various configurations.
  11. richardf
    Joined: May 2013
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    richardf Junior Member

    Thanks for the inputs and suggestions. Paul, I love your boat! But, it is your design. The Bluebird 24 would be perfect, but again, it is someone elses design. I know that designing and building my own boat is strictly for pleasure. I have no intention of ever selling it.
    I have incorporated some of your suggestions and comments. I am strying to keep the entry as sharp as possible, but I am not sure what to do at the stern. A deep V will support more load (motor and stuff), but I would think the sharp departure at the transom would hurt efficiency. To me the canoe is the most efficient displacement hull form, but I want to keep it simple with a hard chine and plywood panels. I don't want to go any narrower on the stern.
    I would appreciate some suggestions concerning the aft bottom shape and reducing the deadrise.
    Here is an updated drawing:

  12. tomas
    Joined: Nov 2012
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    tomas Senior Member

    What is your time estimate to finalize the design, build it, and then get it on the water?
  13. richardf
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    richardf Junior Member

    I hope to start building frames and backbone this December (either my own design or from purchased plans), and launch in the spring of 2015. I will be 74 years old in June 2015. A good age to cruise.
  14. richardf
    Joined: May 2013
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    richardf Junior Member

    I started some rough calculations concerning displacement. First problem was weight to submerge the hull to the center of the chine. Assuming a 7' x 1' triangle for the V bottom and 24 ' length, that is going to take 5000 lbs to get the chine to the water. This was already brought up as a potential problem. I have estimated design displacement to be 3700 pounds (1500 for bare hull, 500 pounds of superstructure, 500 pounds of fixtures, 200 pounds of motor and fuel, and 1000 pounds of people). This leaves me short on where the chine needs to be. What to do? Reduce the deadrise moving aft?

  15. JSL
    Joined: Nov 2012
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    JSL Senior Member

    Welcome to the world of boat design. Buy a book that helps you figure things out.
    Weight and displacement (volume) are always fun. Calculate your scantlings, estimate the weight (and the centers on all 3 axis) and then figure out where it will float. Use the trapezoid rule if you don't want to learn Simpson's Rule.
    If it is too heavy, (floats low), do it all over again: increase the volume, work out the scantlings & weight, and re-check again. Keep doing this until you get a 'balance'.
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