hull design changes, slide VS unwanted cowboy's

Discussion in 'Metal Boat Building' started by emendel, Mar 7, 2017.

  1. emendel
    Joined: Mar 2017
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    Location: smitherss

    emendel Junior Member

    i have an old aluminum boat with an olds 455 Hamilton 753 pump. the boat is 69 inches wide and 21 ft over all length; however the planing surface is 16ft long. the pump has the old flap steering.{unfortunately}

    this boat has a major issue when taking sharper corners at speeds above 18 km in which the *** end passes the nose. it seems like the deeper vee nose digs in and lets the *** raise then slide around it self. this is great fun in lakes, really not fun with 4 hunters and a moose going down stream. end result was sucking lbs of sand and gravel and nearly sinking the boat in a log jam. i would like to correct this issue and i have a few ideas i would like to run by you gents in nz. nothing is out of the realm of possibility. i have a welder and am more than willing to preform any adaptation.

    solution 1: would installing a posi nozzle, keeping the boat on plane in corners stop the nose from droping thus keep the boat tracking properly? or would the added steering benefits of a nozzle only make the problem worse?

    solution 2: would welding 4 lifting strakes on the nose 9 inches off of the center keel and 9 inches off side of the boat [only the front 3/4] force the nose out of the water better in corners? or would it only cause the nose to grab better?

    solution 3: weld 2 square tubes front to back [rails] make the boat track better. on my last boat it cured a spin issue while making the boat not slide in any way. not ideal...

    ideally i would like keep the boats ability to slide while making it more predictable. i would love to get some opinions and learn from your experience

    This boat is used primarily for moose hunting and thus will be hitting rocks, sucking sand, gravel, leaves and sticks regularly i would like to keep the changed as durable as possible. thanks for your consideration cheers. Erik.

    worst case scenario would be cutting the hauls nose out giving it a slower rise however i use this boat 3-5 times a year in the ocean for halibut fishing and i appreciate its ability to cut larger swell.
     

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  2. emendel
    Joined: Mar 2017
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    emendel Junior Member

    strake design

    i was thinking the strakes would should be like this?
     

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

    Your boat needs lateral plane aft, I'd imagine this thing would be a white-knuckle job offshore running with the sea too. I'd be thinking of fitting two shallow skegs, maybe two-thirds of the way out from the centreline, and over say the last few feet of the bottom. Depth maybe 3-4 inches. You'd have to be sure there was no interference with flow into the jet intake. Saying you want to retain the ability to slide, without the radical end reversals, seems like wanting to have your cake and eat it as well, a teensy bit, but I guess you'd have to experiment with the size and depth of the skegs.
     
  4. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Hi Smithers
    As your hull is very flat, it obviously likes washing out.
    I would not put strakes on in the forward part of the hull and leave them out on the back as these front only stringers will only make tripping worse

    I would put 4 strakes, in place, Two on the chine and two midway between the keel and the chine.

    We used a 5 inch by 1 1/2 by 1/4 inch angle. As 5 x 1 1/2 x 1/4 is not available, we purchased 3 x 5 and ran a carbide skil saw down the short leg to make it 1 1/2

    I would cut your leg to make the angle 1 1/4 by 5

    This put the boat on rails, easy to turn, and held in the corners.

    This was for a 10 - 12 degree hull. Yours looks like about 4 degrees, hard to tell.

    I would run them up about 10-12 feet or until the short leg came off the flat of the hull.
    Certainly 10 feet would be easy

    I have no idea why you would want to be able to drift the boat. The first boat that I bought from a company had a narrow beam and 8 degree deadrise, and if you sneezed, you would do a victory roll.

    On the Shotover River in New Zealand, on the tour, they can do 360's but on the Bulkley/Morice, it is asking for trouble. Google Shotover Jet boat as this is pretty amazing. Also google Mott River jet boat running. They have a couple of you tube videos that will show how skinny of water you can run.

    Weld the strakes on continuously . As this will be tough if you cannot roll the boat, you could weld in an aluminum pipe coupling in the back of each strake. Say a 1/2 pipe size. screw in a stainless bushing 1/2 inch to 1/4 female and then install a 1/4 plug into this. This way you can pressure test the weld but more importantly, you can take the 1/4 inch plug out for winter if you have any water get inside the strake.

    You might think about a thinner angle, don't. I have ripped off 3/16 strakes a couple of times hitting a can opener.
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    The OP boat has a shape not ideal for a jet boat, if you have a noticeable forefoot and almost zero deadrise aft, directional stability must be doubtful.
     
  6. ecojet
    Joined: Jan 2017
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    ecojet Junior Member

    Here is the transom of my 19ft Hamilton jet boat even with the deadrise and strakes it's got, the back end was still a little loose underway I put a bash plate with 2 small fins under the jet drive inline with the hull and now runs great.
     

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  7. emendel
    Joined: Mar 2017
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    emendel Junior Member

    So by stringers do you mean strakes ? 1/4 sounds nice and tough which I have no issues with I was kinda eyeing a chunk of 5by 3 angle laying next to my dad's trailer. I have a similar style chine as ecojet is showing at the transom of his boat if I put 1 1/2 turndown on top of the corner chine that's their (won't get into how they welded that but it's... inventive? Likley not somthing I will benifit from messing with its basically flat to the horizon and counters the 5 or 4 degree hull. Adding my 1 1/2 on top might be quite the turn down do you think that theirs a point when it's to much ? Appreciate all the help guys. Ecojet how often do you rip that bash plate off.? Bulkley and Morice are tame compared to the rocks I was smashing that floating bath tub off of on the stikine last year
     
  8. Barry
    Joined: Mar 2002
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    Barry Senior Member

    I had recommended a 1 1/4 by 5 profile , which will turn the strake down. Yes I had quickly typed this as stringer and edited stringer out of the comments
    I agree with your observation regarding Ecojets bash plate.
    And having it attached to the bottom of the jet seems to me that it could cause some problems.
     
  9. emendel
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    emendel Junior Member

    Barry I would love to see some pictures if you could I swear that was kind of the direction I was leaning
     
  10. emendel
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    emendel Junior Member

    Some guys say that this turn down lifts the hull faster do you believe that?
     
  11. ecojet
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    ecojet Junior Member

    Maybe you should go over to the New Zealand jet boat forum and ask them.

    The bash plate is very common on jet boats in NZ.

    My boat is an ocean boat so the bash plate doesn't hit anything.

    Before the bash plate you had to continually correct the steering if you wanted to go straight as the rear end would move around slightly, now it tracks dead straight with no issues at all.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    And your boat was designed for jet propulsion, the OP boat I'd very much doubt was.
     
  13. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The OP's boat is a classic "sea skiff" style of warped bottom and not the best thing for a jet, but not the worst. Directional stability is an issue on all of these, regardless of power type. Lift strakes will add a modest amount of straight line tracking, but only with some speed on. At 18 KPH, the boat is wallowing around pretty bad anyway, constantly "hunting" with the helm, again, regardless of drive type (some are much better than others).

    Other than a spray knocker forward, which can be fairly high up, I'd avoid any additional drag in the forefoot, to keep the bow from "rooting around". I agree with Barry in that, you should look to improve those awful chine extrusions, to address two issues, tripping and lateral area. I disagree in the need for so many strakes. A better one at the chine and a second one about splitting the distance between the centerline and the chine strake, is all I think necessary. The chine strake currently on the boat is very poorly arranged, promoting tripping.

    To address the tripping hazard, the outboard face of the chine strake should be about 45 degrees to perpendicular (canting inboard, not out, like the current one does). This alone might make the boat handle much better, because the boat will not dig her chine in on hard turns, forcing the stern up and in course, the bow down, which causes an ever increasing spiral of events, that screws the boat's handling. The inboard edge of the chine strake should be plumb or nearly so, which will offer effective lateral area, so she'll track better. The inboard strake can just be a length of angle paralleling the centerline, from midship aft to nearly the transom. Stop these short say a few feet, so flow can reattach and separate properly at the transom edge. It would be better if these inboard strakes had the edge facing the centerline standing more upright, for for effective lateral area.

    Forget about the mash plate on that drive, because you'll lose reverse. When the shell drops, it'll blast flow into it and not into the water under the boat.

    Below is a very rough sketch of what you should try. The top one is what you have, an outward facing chine strake at the transom, which is digging in on turns and not helping with lift. The middle one has two extrusions set at 45 degrees, which is easy, but not as efficient as the bottom one, which has it's inboard faces plumb. The bottom one has much more effective lateral, still lets pressure bleed off in the turns, preventing trip and will develop a lot more lift.
     

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  14. emendel
    Joined: Mar 2017
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    emendel Junior Member

    thank you so much! thats what ill try then. i was thinking of extending the chine forward more into the nose in the hopes up bringing the front end up a little sooner what you think of that?
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Nope, extending the chine strake forward, will do little in its current shape. It's not even a good spray knocker. If you want the bow to rise quicker, consider trim changes. That hull should rise quickly, once sufficient speed is gathered up. The bow is fairly bluff and the deadrise flattens very quickly, all producing a lot of dynamic interface with the flow (lift). Inboard forward strakes might help, but you'll likely experience more bow "rooting" in maneuvering. Trim issues may also be playing a serious role in this boat's handling concerns. Do you have pictures of the boat at rest and underway?
     
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