Widened out panga

Discussion in 'Boat Design' started by Jim Allen, Nov 23, 2017.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    One prospect for a boat that can venture into shallows ( the OP mentions 1 foot depth), and be acceptable offshore, would be a moderate deadrise monohedron, with a jet drive. But the ride won't be that great in choppy water, as the cutaway forefoot that is de riguer in a jet boat, plus the medium deadrise, won't iron out the bumps as well as some others.
     
  2. Ilan Voyager
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    Ilan Voyager Senior Member

    Yes, it's just a hard chine small fishing boat. No need of complications like a 40000 bucks jet drive. If you want to go in shallow waters consider using two small outboards. A 50 HP outboard has very little in the water.
    the KISS (keep it simple and stupid) principle applies. No more than 8 feet wide so it's trailerable, light so a cheap trailer is enough, simple outboards with electric tilting adjustment, aluminum propeller so if something is hit the transmission will n0t break. Alu props are very easy to fine tune by an able guy. And "fuse" skegs will protect the propellers if you want to go in shallow waters.
    Although I'm a naval engineer I would not bother and waste time to try to design a small boat for myself, there plenty of good plans for a few bucks, I have another tasks to do than wasting time reinventing the wheel. For a person not having the knowledge buying plans is mandatory, that saves thousands of dollars and hundreds of hours, plus the sadness of throwing a failed boat.
    Choose the simplest shape, monohedron with one strake on each side and the simplest material for a one of boat made in a garage; plywood, glass, epoxy.
    And buy good plans well drawn with offsets, plenty of drawings of the details and a complete list of materials, it's worth the modest price asked by the designer.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    What is a "fuse" skeg ?
     
  4. Ilan Voyager
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    Ilan Voyager Senior Member

    A skeg or fin easily replaceable after a hit destined to protect a propeller or other thing and/or give some directional effect . Generally screwed at the bottom of the hull. Strong enough to offer some protection of the desired item, not enough to destroy the hull if broken, it will absorb most of the hit energy
    When beaching well placed fuse skegs remind to the oblivious captain of the panga; have you tilted the outboards? A very common and costly accident in our beaches, not always innocent. And made easy to take out before trailering.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Skegs, by their nature should be considered a "consumable" or sacrificial element. I make them tough enough to hold up the boat if trailered or beached, but don't include them in sheathing schedules that include the hull. Additionally, I'll spec a half oval, but lightly fastened over bedding, not bonded, though fasteners may have bonded holes. These small, light rub strip fasteners are intended to shear clean, so it does it's job, but if the impact is hard enough it falls off, leaving what's left of the skeg for repairs. I lastly tend to design them without through fasteners, unless they provide some effective lateral area that must be maintained. The idea, to prevent leaks at the through fasteners.

    I think what Iian may be referring to are traditional bottom rub strips, which often are little more than a 1x2 lightly screwed to the bottom, with a half oval screw to it. You see these a lot on flat bottoms and they offer some directional stability as well, if shaped properly. These are wisely designed as described above, to prevent major damage to the main hull, but offer abrasion and impact protection to the bottom.
     
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    I have used the two variants you have described. Rub strips are very useful for small boats, but the skegs I deviced were used to warn oblivious or let's say by euphemism indelicate hired captains of the commercial dive boats. Broken transmissions and even exploded legs of the outboards are not uncommon, it's a very expensive affair.
    These boats pick the equipments and the divers always on the same authorized beach, the closest to the dive shop. So the angle and depth of the beach are known, and it's easy to size and place the skegs, or better said delta shaped fins in such a way that the skegs will touch the sand long before the propellers thus warning the captain that he is going too far in every meaning if the word, so he has no excuse.
    As the hulls are made with a "frozen cod" of lots of orthophthalic polyester resin and mat with some scarce cloth, of a thickness of somewhere between 5/16 to 1/2 inch at best, the surest way was to install a wide aluminum base 3/16 thick bolted through the hull with a wider alu counterplate inside and lots of 5200 goey. and no sharp corners, oval os the best shape. The alu is a T6061 state 0 or 1, very malleable. So the hull is protected with no hard points.
    On this base was screwed the fin made in a plastic like nylon with glass fiber. Plastics are very predictable in strength, do not rot, do not need paint, resist well to abrasion and can be shaped with ordinary tools. Calculations are straightforward. That worked as designed and lots of propellers have been saved.
    Most captains liked these skegs as warning devices specially when the sea was choppy with breaking waves, and for the directional stability. Also manoeuvering was improved as the flat bottom had now a pivot point.
    The induced drag was negligible on boats running at the low 20 knots over short trips. I made a survey of the gas consumption and nothing significant was found. I would not say the same on 30 knots boats on long trips.
     
  7. johnnythefish
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    johnnythefish Junior Member

    Would either of these not be a starting point for the OP...

    | Boat Plans For Amateurs https://bateau.com/proddetail.php?prod=PG25

    | Boat Plans For Amateurs https://bateau.com/proddetail.php?prod=GS28

    Also could one not increase carrying capacity for the same draft by having a longer Panga rather than widening one and then essentially loosing the appeal of the Panga in the first place - an efficient shallow draft vessel, capable of running well in a variety of speeds - there by allowing you to choose a speed that is right for the sea conditions.
     
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  8. Ilan Voyager
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    Ilan Voyager Senior Member

    You're right on such shapes it's easier to add a foot of length rather than trying to wide. The links to the plans are very interesting specially the 28 feet, a very simple monohedron. The builder won't struggle with the plywood.
    That shows what you get with 195 bucks, the price of a low end smartphone. I inagine someone with no knowledge trying to make a similar job...
    32 drawings. CNC files. Calculations and scantlings. Methodology with manuals. List of basic materials for the hull.
    The explanations are correct and I agree that is designed for mid twenties knots with 100-120 HP. It's not a speed boat above 150 HP you're wasting gas.
    A simple basic fishing boat. There many possibilities depending on the use and local conditions like using 2 small outboards and skegs for very shallow waters, getting also improved maneuverability.
    I made similar boats in Mexico and Dominican Republic in monolithic GRP plus Coremat. No need of a mold, you use that I call the placo-plastic method.
     
    Last edited: Nov 29, 2017
  9. wavepropulsion
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    wavepropulsion Pirate Member

    Motor Boats 16' to 20' http://www.selway-fisher.com/Mc1620.htm
    Paul Fisher has several models as the first in this page. Described as load carrier or for speed. How the ride and fuel economy compared to a V bottom? The beam is more or less what the initial poster asked, and the bottom looks like a Panga. Can be lenghtened too but I don't know how can affect the boat by having the beam more to the bow. I had a boat with a similar bottom and they are very forgiving in beam seas, but can pound a bit above the ''panga speed''. I don't think is unseaworthy. Planes very easily and has a very shallow draft, floats in dew and this models are classifyed off-shore by the designer (who has a good reputation). It is really an advantage a V hull at this speeds?
    Check the Power 2 also Motor Boats 21' to 30' http://www.selway-fisher.com/Mc2130.htm With three feet added straight to the rear and twin 40's does 30 knots in the Irish Sea with a team of divers.
     
    Last edited: Dec 14, 2017 at 5:43 PM
  10. Ilan Voyager
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    Ilan Voyager Senior Member

    None of the plans of the limks is interesting. I would not try a Mexican panga im Mer d'Iroise Brittany France even by nice weather. I have a poor health but I do not want to lose the remaining prematurely.
    Flat bottoms are complications in boat building, except in boxy doris.. First they lack cruelly of rigidity so you have to use or heavy scantlings or a lot of structure. Second they ruin the water entries, that become far too full unless you enter in structural and building complications. Third it obliges to other complications for having the mandatory strakes and fourth one bucket of water inside and you have water splashing everywhere.
    On the other side a light vee is symmetric, that helps when you're using a cheap fast made steel female half jig, To get the other side you simply rotate of 180 degrees the elements of the jig on the reference centerline.
    The V is a triangular figure naturally rigid with little structure The water collects at the bottom of the V and is easily pumped out. By simple torsion of the panels and a steeper V in front you'll get good slim entry lines and a correct bow. If you use "pressure curves" in the design the placement of the panels in the jig becomes indecently easy even with a very evolutive shape. Brief. life becomes easier for the builder and hydrodynamics are better.
     
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  11. wavepropulsion
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    wavepropulsion Pirate Member

    I can't argue with you Ilan (because your great knowledge, I learnt from you about long light planing hulls some theory I appreciate, by reading your posts). I recognize I'm very ignorant, but I see there are two school of toughts about boat bottoms. I think about the Mini Transat Scow specially (sailing upright most of the time), or some brands of high performance powerboats (don't remember if Allison) using a wide delta pad, a compromise between a flat bottom and V bottom. I don't know if this kind of bottom is called flat, U bottom or trapezoidal. Transonic hull claims good motions in any sea compared to any other hull shape, no idea, just read some papers.
    The flattish bottom will plane at less speed and skim over the water, while the V will cut the waves and pound the same but at faster speed. I believe the V hull can be structurally stronger, and will have a different behavior, not ever better. At ten to twelve knots in a flattish planing hull you can ride comfortably seas a V bottom needs to slow down to displacement speeds where generally rolls a lot (because not ever can plane at over 25 knots) and the heavyer stern is more exposed to be flood and sink the boat. At all speeds below planing, a V bottom pays a price too, or in his behavior, or in building complications to avoid it.
    I don't say the trapezoidal bottom is better, but has its niche of convenience.
    I don't like to do this a discussion (again) of flat vs. V, but what the person who created this post asked for, is a boat that can run offshore, with great carrying capacity, and shallow water capabilty. Being a working boat, fuel economy and economy of rigging can be important too, is not the same to carry a 50 hp than a 100 outboard, and is another contribution to seaworthiness to have less weight at the stern. He asked for a wider Panga, surely has some experience.
    I never had much water in the bilges, but all water goes to the stern where is the pump. In the american Panga forums they discuss about ''americanized'' pangas compared to mexicans, and they claim are very seakindly at speeds of around 15 to 18 knots (Panga Speed they call) or being at home at displacement speeds (both american coasts, east and west).
     
    Last edited: Dec 15, 2017 at 1:43 PM
  12. Ilan Voyager
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    Ilan Voyager Senior Member

    We are talking about the solutions for a small fishing boat that an amateur can build from a good set of plans, running in the range of the 20-30 knots with outboards, made cheap and fast from a flat material on a female jig -everybody will think of plywood, I'll add GRP plates as marine plywood is a rare and scarce material in the world- and I'll stay in this context, as the thread started from widening a panga, the worldwide symbol of the small cheap fishing boat.
    It is not a general discussion about V or flat hulls, In fact this discussion is useless as the deep V hull and its variants apply only in a very narrow range of boats, mostly racers and the "yachty" imitations of racers. The thread is about a working boat, not a yacht.
    I started from a monohedron with a 10 to 12 degrees V ,a very moderate V, at the transom. That is a ordinary shape in working boats. it has good hydrodynamics and it's easy to build. It can be tweaked, and with the help of some simplified tensor calculus, very interesting shapes can be obtained from flat sheets.
    The moderate V monohedron has a very wide range of applications, from the 20 feet fishing boat to the 170 feet patrol boat at my knowledge. I'll show a very extreme example of such a monohedron nicely tweaked by Didiert Marchand, naval architect in France. It's the direct descendant of a serie of studies made around 1980, partly by the French Navy for the Public Service Patrol Boat
    It's the new 60 feet rescue boat of the SNSM on France, it's a beauty. The boat has shown extraordinary capabilities in very hard sea. It can run at more than 20 knots in a state 9 sea. The bow is not a bulbous bow it's a rostrum bow, designed to cut the waves. The shape of the underwater hull part can be used for a 28 feet by 8 feet fishing boat with a few mods. There are plenty of informations on these images...



    SNSM1.png SNSM2.png SNSM3.jpg SNSM3.png
     
  13. wavepropulsion
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    wavepropulsion Pirate Member

     
    Last edited: Dec 16, 2017 at 12:32 PM

  14. Barry
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    Barry Senior Member

    Voyager
    Can you send me a link to a site that shows GRP plates characteristics, strength, flex, etc. The only thing I have found are GRP plates as flooring etc.
    And how do you make up the butt joints so that the stresses/loads can transfer between plates.
    If the OP is going this far, then why not C Flex and get the longitudinal/transverse strength issues out of the way

    If GRP plates are expensive as someone as I believe you have stated, why not just build out of aluminum
    Certainly I am biased toward aluminum but the advantages are:
    1) while the material MIGHT be a bit more expensive than wood, fibreglass, GRP plate, OVERALL the cost may be cheaper. Ie compared to building with wood, no glue, no paint, easier build and fit, less time to build, the same tools as woodworking tools, with the exception of the welder. And you have a hull that could last 50 years or more with excellent resale value.

    2) If you are not a welder, you can easily learn to make tack welds so that you can fit up the components, tack them together and have a certified welder do the weld.
    Our 24 foot aluminum hulls took us 80 man hours to build, would require about 8 hours of actual welding time. The rest is fitting. ( complete enclosed front deck, jet protector, 4 lift strakes, full center opening windshield, (80 hours for the pure hull and another 120-140 hours for tanks, Dura deck covered floors, instrumentation, engine/pump installation, fuel tanks, seating, etc)

    3) pretty much any plan that you can build out of plywood can be used to build out of aluminum

    One main advantage of aluminum is the ease of making STONG joints in very little time.
    Equipment wise,
    Minimum : a skill saw with a 60 - 80 tooth carbide blade, a 4 1/2 inch grinder with cut off blades and sanding discs, a jig saw, hand drill
    Moderate: all of the above and a bandsaw, fixed belt sander, , makes fitting easier
    Buy the welder, used, then sell in when you are done.

    For the first timer, of course you would have to build an extremely rough, male jig, which can be made out of wood. By rough, you are only looking to hold the plate for tacking, so maybe another 30 - 40 hours here OR buy a set of dxf files from a plan supplier, have the sheets cut then you only need a strong back to build the boat. Much quicker of course

    A note on cheap. A discussion point that comes up frequently are threads where people want seem to want to build a boat as least expensive as possible and what often is lost is that the cheap way might result in a boat with no resale value and many more hours of time to build. I understand that some people enjoy say working with wood etc and it becomes a labor of love. Emphasis on labor, :).
    Often when these discussions start and often from people who never have built a boat, the focus is on the initial cost of materials, not the incidental costs to build. Glue, primer, paint, and the ongoing expense of maintenance, ( ignoring time,) these costs can exceed other methods of build which appear to be initially cheaper.
     
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