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Flatbottom Dory: Speed, seaworthy?
Hi,
I want to design and build a "riverboat" for the Fraser River, with some .... "unique" design considerations (eg I want it to look ugly because it will be on a "questionable" dock and I don't want it stolen!). Basically I'm looking for something between an east-coast fishing dory and Bogie's "African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard and probably not Stitch'n'glue. Anyway, I need some anecdotal feedback: First, a 16ft boat has a theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats (such as my 12ft alum) that exceeds hull speed without truly planing (semi-plane?) Does anyone have some performance numbers for 14-16ft flat-bottomed skiff as to how fast they go before planing? I'm looking at maybe 6-10hp engine. Second, I'm unfamiliar with how a flat-bottom hull performs in waves - are they seaworthy? Thanks for any comments, stories, etc! Lloyd Sumpter |
Flatbottom Dory: Speed, seaworthy?
"Lloyd Sumpter" ) writes:
Anyway, I need some anecdotal feedback: First, a 16ft boat has a theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats (such as my 12ft alum) that exceeds hull speed without truly planing (semi-plane?) Does anyone have some performance numbers for 14-16ft flat-bottomed skiff as to how fast they go before planing? I'm looking at maybe 6-10hp engine. Second, I'm unfamiliar with how a flat-bottom hull performs in waves - are they seaworthy? Thanks for any comments, stories, etc! Lloyd Sumpter If you want a planing boat following might be of use .... If you don't want the boat to plane it might still be of use ... If you don't want a planing boat then it should be long and narrow for good fuel efficiency. TF Jones writes that a boat should plane with 1 hp for every 40 lb displacement. That should give you some idea of now big an engine you'd need. Flat bottom skiffs and garveys plane good. The back end of the boat has to be broad and flat. Sorry, I don't know how much flat bottom you'd need to plane a given displacement. Planing boats are not good in rough water. You need smooth water to plane in. You can increase "seaworthiness" by giving the boat high sides and higher bow with the sides raked to keep spray from coming on board. Flat bottom planing boats slap the waves. That can be pretty annoying for some people. That's why "ocean" skiffs have "V" bows giving 'way to flat bottoms aft. The "V" cuts the waves instead of slapping them. There are lots of old plans for these plywood planing skiffs. Any planing power boat needs a good strong bottom to take the pounding. Feel free to copy and use the Skiff program under Boats on my website to try different dimensions. Its not for planing hulls because it assumes the rise in the bottom aft. You can use it for a dory by making the transom very small, or anything you can imagine in between a dory and a skiff, like a drift boat. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
Flatbottom Dory: Speed, seaworthy?
Basically, a flat bottom boat is always on a plane and can exceed "hull"
speed easily because of that. As for ride, rough. Will pound at any kind of speed but plenty seaworthy (most not good in a following sea) as evidenced by all the dories out there. Gordon "Lloyd Sumpter" wrote in message ... Hi, I want to design and build a "riverboat" for the Fraser River, with some ... "unique" design considerations (eg I want it to look ugly because it will be on a "questionable" dock and I don't want it stolen!). Basically I'm looking for something between an east-coast fishing dory and Bogie's "African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard and probably not Stitch'n'glue. Anyway, I need some anecdotal feedback: First, a 16ft boat has a theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats (such as my 12ft alum) that exceeds hull speed without truly planing (semi-plane?) Does anyone have some performance numbers for 14-16ft flat-bottomed skiff as to how fast they go before planing? I'm looking at maybe 6-10hp engine. Second, I'm unfamiliar with how a flat-bottom hull performs in waves - are they seaworthy? Thanks for any comments, stories, etc! Lloyd Sumpter |
Flatbottom Dory: Speed, seaworthy?
Hi Lloyd, I had a couple of flat bottom, plywood fishing boats as a kid growing up on a lake. The 12' would plane with a 3 hp Johnson. The 14' would run like a a scalded dog with a 15hp Merc. (Kiefhoffer) I do recall that loading it up with 6 or 8 other kids kept in displacement mode. Mostly due to the overload. Made a great bow wave! Alas. the days of youth. -- Capt. Frank __c \ _ | \_ __\_| oooo \_____ ~~~~|______________/ ~~~~~ www.home.earthlink.net/~aartworks "Lloyd Sumpter" wrote in message ... Hi, I want to design and build a "riverboat" for the Fraser River, with some ... "unique" design considerations (eg I want it to look ugly because it will be on a "questionable" dock and I don't want it stolen!). Basically I'm looking for something between an east-coast fishing dory and Bogie's "African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard and probably not Stitch'n'glue. Anyway, I need some anecdotal feedback: First, a 16ft boat has a theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats (such as my 12ft alum) that exceeds hull speed without truly planing (semi-plane?) Does anyone have some performance numbers for 14-16ft flat-bottomed skiff as to how fast they go before planing? I'm looking at maybe 6-10hp engine. Second, I'm unfamiliar with how a flat-bottom hull performs in waves - are they seaworthy? Thanks for any comments, stories, etc! Lloyd Sumpter |
Flatbottom Dory: Speed, seaworthy?
"Gordon" ) writes:
Basically, a flat bottom boat is always on a plane and can exceed "hull" speed easily because of that. Shallow draft light displacement boats don't have much displaced water to push aside. It doesn't take a lot of power to push them beyond "hull" speed without actually planing. Canoes and kayaks are like that, and shallow draft skiffs. Dorys have narrow bottoms and tend to sit too low in the water to be really shallow draft. It doesn't take much to lift a light displacement, shallow draft, wide bottom skiff or garvey onto a plane. As for ride, rough. Will pound at any kind of speed but plenty seaworthy (most not good in a following sea) as evidenced by all the dories out there. Gordon Its the narrow bottom, deeper draft, and high sides which make the banks style dory more seaworthy. John Gardiner's "Dory Book" shows the 19 ft inboard St Pierre fishing dory from the French islands in the Gulf of St Lawrence. I think he wrote that the French government documented the plan and made it avaiable cheap to the fishermen there. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
Flatbottom Dory: Speed, seaworthy?
crap, I just spent half hour addressing your questions and then my
google **** the bed... I will try again tonight, in the meantime see: http://smallboats.com/stanley_sie.htm Scotty, sorry |
Flatbottom Dory: Speed, seaworthy?
"Lloyd Sumpter" wrote in message ...
Hi, I want to design and build a "riverboat" for the Fraser River, with some ... "unique" design considerations (eg I want it to look ugly because it will be on a "questionable" dock and I don't want it stolen!). Basically I'm looking for something between an east-coast fishing dory and Bogie's "African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard and probably not Stitch'n'glue. Anyway, I need some anecdotal feedback: First, a 16ft boat has a theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats (such as my 12ft alum) that exceeds hull speed without truly planing (semi-plane?) Does anyone have some performance numbers for 14-16ft flat-bottomed skiff as to how fast they go before planing? I'm looking at maybe 6-10hp engine. Second, I'm unfamiliar with how a flat-bottom hull performs in waves - are they seaworthy? Thanks for any comments, stories, etc! Lloyd Sumpter OK, a ten horse might get the 14-16 on plane but with effort and light loads. You probably should look at a 15. My 12 foot skiff noted earlier in the post planes at about 12 mph with a load of me and another 300 lbs or so. A pointy skiff blends in well, holds a tremendous amount of weight, are very stable for fishing and such, a 14 footer will hold two to three kids on one gunnel and still not near flip over, they can be run all day long at a strong hull speed with a 5 horse or even a three on a lake, a 14 will still row nicely with properly sized oars, beach nicely... A pointy skiff of typical design with flat sides and bottom will plane off easily and can be a lot of fun but for practical use, you will not spend to much time on plane. At high speeds you will get somewhat if not all the way airborne which is waaaaaaay cool, but these boats do not "fly" well and a slight yaw and roll means you catch a sharp edge in a wave and abrubtly turn or in extreme cases roll (which btw is not as bad as it sounds if you are prepared for it and just out playing in the waves;)), at plane you can have a condition called "chine walk" which can lead to rollover, flat sided pointy skiffs are very wet boats and if you or your fishing partner are sensitive to being wet all day, do not build one, even in a slight breeze at hull speed you get spray in most typical instances. Flat bottom skiffs slap, even at slow speeds (typical with little rocker) and on plane this slapping means catching edges and putting up spray. Flat sided pointy skiffs don't usually have a lot of bearing up front so they tend to dive into or through waves, taking a lot of water... especially when you don't expect it like the 9yo decides to go up front abruptly for chips and the dog decides to join her at about 8 mph... nice wooden swimming pool in the middle of the lake! Ok, sounds like I hate these boats, on the contrary, I have made my business on them. I just like to see that folks who get them, know what they are getting in to. Did I say, these are wet boats, period! That being said, here is what I would do if I were you and still want a pointy skiff: Go with the 14 footer. Make it 6.5 to 7 feet wide in the center and 6 inches narrower in the transom. Cut a couple of pieces of 1/4 inch plywood and lay them lengthwise, tack em' down. On one end draw a point 20 inches up and put a nail in with 1/2 inch left visible. Go to the other end, come in two feet (for a 14 footer) and put a nail 28 inches up in a similar fashion. Connect the two nails and lay a line. Cut out your side panels and butt joint them together, cut back wider ends (bow) 30 degrees and the stern say, 10-15 degrees. Take a four foot 4x4 and knock off two chunks at 30 degrees and make a stem. Sharpen the stem and drive it into the ground at a 30 degree angle, where you will build your hull and attach your side panels to it. Make a 24 inch high transom or 2x4's and 3/4 inch plywood and attach two stakes to it temporarily so you can drive it into the ground, 14 feet from your stem! A ten degree rake from bottom to top of transom should do for 10 degrees sides at the transom. Make a quick jig of scrap to wrap the sides around see: http://rbbpix.com/images/stanley_sie_03_450.jpg If you wish your chine logs (1x4, where sides will meet bottom) to be inside of the hull, make notches in your jig to accept the 1x4's, make the notches oversize and use wedges later to make up for the spaces. Using whatever means possible, wrap the side panels around the jig and attach to the transom, now it starts to look like a boat! Apply your chine logs, inside or outside, yes outside, looks funny like you wanted ;) and it is actually much easier then trying to size and force inside gunnels without long ends to hold on to and remove later as in outer chine logs. Many Bolger boats have the "logs" on the outside of the hull, anyway, attach your chine logs. Well, seems simple don't it and it just begun. Anyway, stay tuned as tonight I will try to get to the bottom, seating, flotation, motormount etc. For now, it is beautiful out there today and I got an itch... Scotty |
Flatbottom Dory: Speed, seaworthy?
On 29 Feb 2004 11:10:25 -0800, (Backyard Renegade) wrote:
OK, a ten horse might get the 14-16 on plane but with effort and light loads. You probably should look at a 15. Main thing though, he wants it to go "pooketa-pooketa-pooketa". Is it possible to do that and plane at the same time? Rick |
Flatbottom Dory: Speed, seaworthy?
) writes:
Main thing though, he wants it to go "pooketa-pooketa-pooketa". Is it possible to do that and plane at the same time? definitely, if he doesn't mind doing the "pkta-pkta-pkta" himself while the boat does the planing. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
Flatbottom Dory: Speed, seaworthy?
|
Flatbottom Dory: Speed, seaworthy?
"Lloyd Sumpter" wrote in message
Ok, where were we? Oh yeah, the bottom. Lay your bottom panels across the boat and mark the edges on the hull, mark the bottom pieces for cutting. leave at least 1/4" inch extra to be removed later. This helps nails go in without splitting out the edges and just makes things easier. Now fasten 4x4's across the chine logs, flush with the bottom, and where they will be the seams for the bottom panels. So, there should be a crossmember at 4 feet from the transom, 8 feet, 12, I think you get it now. fasten and glue the bottom panels to the stem, transom, chinelogs, crossmembers. Note, it is a good idea to cut some small notches in what will be the bottom of the crossmembers so as to allow water to flow fore and aft. I usually put a strip or two of 4" fiberglass tape bedded in resin on the outside seams of the boat, mostly to protect the edges of the plywood, in this build, this step is not structural so it is a matter of choice. Put on a skeg or two and then flip her upright. Fasten some chunks of 2x2 to the sides, ten inches up from the floor and attach some seats. You should take a chunk of 2x6 from seat to floor in the center to support the width of the seat top. Double up the plywood on the inside of the bottom with a 3x8x3/4" plate for the seat support to sit on. Next put in a breast hook and quarter knees. Rabbit the front and back of the seats to accept a 1/4" plywood to cover the foam which you should stuff under the seats. Fasten on the gunnels 1x4 or 2x6 for more strength. 2x6's can be bent in a few days by simply laying them over a big rock and putting weight on either end... It wont take much, a cinder block or two in each end will do the trick. Put on the hardware, paint, and float. Ok, we got a boat simple right? Uh, no you say? You don't understand parts or I am not complete enough? That's ok.. Get the book "Instant Boats" from Dynamite Payson at instantboats.com for about 20 bucks and this will all make sense in a matter of a couple of hours of reading. Note, Payson is a client of mine in another business. Anyway, happy building and as always, I can be contacted directly at my website if you have any specific questions. Later guys, getting started about 6 weeks early this year, I will hopefully have some nice pic's of the coming projects. Scotty from SmallBoats.com |
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