Welded Aluminum Shallow Water Boat

Discussion in 'Boat Design' started by dick stave, Jan 2, 2005.

  1. dick stave
    Joined: Dec 2004
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    Location: MISSION B.C. CANADA

    dick stave Senior Member

    Im planning to build a new boat this winter for fishing the Fraser river and its
    sloughs.The fraser is about 200 yards wide and holds 5 species of pacific salmon,white sturgeon, and trout.During freshet, in the early season,there is plenty of depth to run a prop boat.In august the river drops and many props
    become pretzels. simple solution;a jet boat and avoid tilling the gravel bottom.Outboard jets are expensive,noisy,and gas guzzlers.Hence my search
    for a shallow water prop design.I would like to build in the 14-16 ft. range a flat bottom,or shallow vee boat capable of running in a foot or two of water witha 25-35 hp outboard prop.I have looked at jon boats on the web [G3,Alumacraft,Xpress etc.]and was impressed with the claims of 4" draft on
    jackplated 27" transoms.I have also read that similar results can be achieved
    with setback and raising outboards.Would a tunnel jon suit my needs? I followed Dan Ayos thread on tunnel design and have contacted him.Can anyone else shed light on shallow draft boat designs/ rigging? d.s.
  2. CDBarry
    Joined: Nov 2002
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    Location: Maryland

    CDBarry Senior Member

    You may want to look at getting a engine-jet unit out of a jet ski.
  3. Thunderhead19
    Joined: Sep 2003
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    Location: British Columbia, Canada

    Thunderhead19 Senior Member

    I have heard of people sucking small gravel into the jet intake in shallows too. The prop seems to be a good idea. Maybe even a paddle-wheel arrangement (seems like the perfect thing for shallow rivers, eh?). Flat bottom boats can achieve very shallow drafts for their carrying capacity. You might be able to use a slow turning prop with a big surface area partially submerged, akin to a surface drive. When you put a tunnel into a hull, particularly in a small boat you sacrifice valuable buoyancy. In a small boat like you want, you might just be able to use a regular outboard with a shallow draft johnboat. You could put an extended skeg on the leg to warn you when you're getting into trouble, maybe even rig it so your motor tilts up when the skeg drags on something (reversing would be a bugger though, if the leg is free).
  4. I always run any outboard motor in the unlocked position. Safer foward, only a lift up in reverse, slow- approaching the dock or lock it down then.
  5. Sean Herron
    Joined: May 2004
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    Location: Richmond, BC, CA.

    Sean Herron Senior Member

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  6. dick stave
    Joined: Dec 2004
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    Location: MISSION B.C. CANADA

    dick stave Senior Member

    Thanks for your replies.Im surprised to see responses from B.C. boys,but I need to enlist some Texas and Louisiana expertise if Im gonna build this skiff. Ive uncovered some tunnel guidlines at the gulf coast fishermans website; Eg. tunnels work best in a
    ratio of 12:1 [length- height]. Five sided or round not more than one third the hull length.A short tunnel is hard to prime or function at low speeds.Square tunnels cause turbulence and drag.Im surprised by the square tunnel statement because most of the production jons have tunnels [although tapered]that are fairly square.Any input?
    I came across an article on the Henderson flats skiff :
    http:// www.whopperstopper.net/readingroom/hendersonskiff.htm This design caught my attention[could be easily adapted to aluminum ]although im not sure it has a vee bow entry which I want.Anybody out there built boats like these?Anyways, im leaning towards a 16 footer[even though it will be a real tight fit in my shop].
    Thanks again for your input, d.s.
  7. Have you thought about the various rigid bottomed inflatables? Low draft. Round tunnel is always right, unless your prop is not. A light, 400# boat, can hide a lot of poor design and still be enjoyable.The fish do not live in 6" of water.
  8. dick stave
    Joined: Dec 2004
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    Location: MISSION B.C. CANADA

    dick stave Senior Member

    Thanks for your reply,
    I pretty much have my mind made up im going ahead with a monohull welded jon boat design.I have looked at countless sights on the web and Im finding that hard numbers for a 16 ft. tunnel jon are scarce.I designed and built a 16 ft. shallow deadrise center console in 2001 with pretty good success so im real comfortable with the fabrication aspect [I do it for a living ].Im going to keep digging until I come up
    with the formula for this boat. the tunnel shape and dimensions are my hurdle at this point.Has anyone read "secrets of tunnel boat design" by aeromarineresearch? Does it contain info. specific to these types of tunnels sometimes called pocket drives? Again thanks for your help.
    Regards, d.s.
  9. Sean Herron
    Joined: May 2004
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    Location: Richmond, BC, CA.

    Sean Herron Senior Member

    Last of the 'sparkling wine'...


    See enclosed pics from http://www.mowdyboats.com ...

    I am not sure whether you are looking for a cat hull or more of a Vee'd 'flats boat'...

    Any way I am just now out on the 'last of the sparkling wine' so I am no good to anyone...

    Also see http://www.copernic.com - it is a downloadable and still free - (basic version) - local proggie that will search multiple data bases...

    Priming of the tunnel is not relevant if it is full of water - all below waterline - so long as prop is same - trouble is manueverabilty (spelling) if the O/B is mounted in tunnel and cannot wash to sides to push the stern about...

    With some of these boats you have to think 'Arneson drive' or semi piercing - very hard on an outboard that wants to feel some proper loading and you have to watch the coolant water pick up level (MOST IMPORTANT) - but they make them work - I would be inclined towards cheap *** (ahem) plastic and aluminum props and plenty spares - YUP...

    You could even download that http://carlsondesign.com/ freeware 'hulls' bit that will output developed panels and find my VERY old 'flats 16' - square tunnel - little side wash unless transom mount...

    The trick - (per the 'Yanks') - is a combo of keeping the tunnel small - just enough to keep good flow over the prop - and wide flanks for displacement to hold the bloody motor up - makes sense...

    You may also find those crazy 'sprint boats' very interesting - another world...

    Lastly - Fraser Pacific salmon run in less than 4 inches of current - YUP - so forget the suit - and tie some flies...

    Also http://texassaltwaterfishing.com/transportboats/transhowroom.cfm ...

    Where is my drink... :)



    Attached Files:

  10. You are doing the right thing with the Alum. JON . Plus you can get insured! and pass a USCG inspection. Enjoy it.
  11. dick stave
    Joined: Dec 2004
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    Location: MISSION B.C. CANADA

    dick stave Senior Member

    Thanks for your responses.Im hoping to start drawing the new boat this weekend.
    I decided to go with 16 ft. o.a.l.,48" bottom,21" sides,27" transom,7" h. x 14"w. x 48" l
    5 sided tunnel,30 hp tiller power on 4" setback 7" elevated jackplate.All fabrication will
    be done by myself.All materials .125 5052.Im gonna go with a vee bow entry transitioning to flat bottom at the stern.I emailed ALUMACRAFT and asked them what
    there tunnel dimensions were posing as a potential buyer. Iwonder if theyll give it up.
    How big of a secret are these tunnels anyway? If anyone has any imput on my boat
    dimensions/concept and especially my tunnel dimensions it would be greatly appreciated [never got the southern technical advice I requested]. Anyways, thanks
    again for your support.
    regards, d.s.
    p.s. cheers Sean [its friday night ]
  12. Go to a ALUMACRAFT dealer. He could care less about you measuring the whole boat. He only sees you as a possible customer.
  13. artemis
    Joined: Oct 2004
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    Location: USA

    artemis Steamboater

    Hopefully you'll open this before you start designing. Take a look at the Atkin Boat Design site at http://www.atkinboatplans.com Billy Atkin (and son John) did a lot of good designs. If you look under the inboard utilities & runabouts you'll find designs that could be easily developed in aluminum. And if you want a boat that can also run up on the gravel shingle, particularly look at his Sea Bright Skiff tunnel designs (also protect the propeller really well). One nice thing about Atkin designs - they're tried and tested and the ones on the website are intended for home builders. All the Sea Bright tunnel drives handle rough water (as much as you'll find in your fishing area) very well. And the HP needed to drive them at 18+ mph is remarkly small.

    Ron Fossum, formerly from Puget Sound
  14. bsmit24
    Joined: Mar 2005
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    Location: Louisiana

    bsmit24 Junior Member

    tunnel design info seems to be hard to come by. I assume that the shape you are using is half of a cone so that both the width and the height gets smaller. Does anyone make a tunnel so that the area stays realatively constant throughout its lenght. It would seem that it would help ram water into the void to fill the tunnel no matter its height (similar to some air inducted hoods). Is there any guidence on the tunnel to hull shape, a smooth taper or an small step?

  15. Gilbert
    Joined: Aug 2004
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    Location: Cathlamet, WA

    Gilbert Senior Member

    Hi Dick,
    I missed seeing this thread earlier so maybe your boat is done now and my comment will be of no use. I recently computer lofted a Florida flats boat to Ken Swan's design. It is a 15 footer and the beam on the bottom at the transom is a little over 5 feet. The customer felt this much beam was very important and I'm guessing it would be on your boat as well. There was no tunnel. He described their practice of rigging a two by four on edge somehow under the outboard bracket for running slow in shallows. If it's too shallow for that they pole or get out and push. Reminds me of some of the boating I did as a kid in the tidal sloughs here on the Columbia.
    Hope everything turns out well.
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