Removable Keel...

Discussion in 'Boat Design' started by John Shepherd, Jul 8, 2019.

  1. John Shepherd
    Joined: Jul 2019
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    Location: UK

    John Shepherd Junior Member

    I know I know, but bear with me. I've just joined and read with interest some of the historic posts regarding adding keels to planing hulls. I have a planing hull and she's great at sea but a pain on the river as she wanders from side to side. I had hoped that a duo prop might solve this problem but I'm lead to believe that it won't.
    I was wondering if I could make a long simple keel which essentially straps onto the hull when I'm in the water. I know it might sound daft, but not as daft as you might imagine. If I had a keel then added some rubber or other straps with the right length and designed these to clip onto the side of boat via rails or some other method then I could simply add and remove the keel as needed. But the whole idea of the keel is only to use on the river at around 6knts so stress would be extremely minimal but would this give be better directional stability when cruising?
    Thanks.
     
  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Welcome to the forum.

    This is a great place to bounce ideas around.

    My greatest concern is that a clip on keel could come undone under way. Or worse, shift out of alignment causing a loss of directional control.

    What is the make and model of your boat?
    Someone may have already solved your problem.
     
  3. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    a pain on the river as she wanders from side to side
    could you describe the motion. Heeling side to side?... changing direction side to side ? Is it worse going up-stream or down?
     
    Last edited: Jul 8, 2019
  4. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Otherwise, know as LeeBoards perhaps?

    That's gotta be the easiest solution.
     
    tpenfield likes this.
  5. John Shepherd
    Joined: Jul 2019
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    Location: UK

    John Shepherd Junior Member

    Thanks for taking the time to reply. I don't have any images to show, but I thought it a known issue that planing boats will gently change direction and 'wander' when at slow displacement speeds - they all pretty much all seem to do it. A duo prop helps to stop this and the problem is evident on more shallow deadrise hulls (I think), so US boats such as Sea Ray or Bayliners for example are much more prone. Some planing fast fishers, the Antares 750 for example has a small keel to aid slow speed directional stability for trolling I guess. If you google this boat via images you'll see what I mean. It's this feature I was thinking of replicating. It would have to be strong and strapped in place well so as not to move, but as displacement speed the stresses would be extremely minimal. removing the keel for faster (above 6knts) would be easy but the adding of the device would be tricky and I can only see it being fed in from the bow while holding the straps so it can be fed down the hull under the water until it's in the right place. I know what I mean in my mind anyway...
     
  6. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    Welcome , How about a protection strip that runs the full length of the keel, and or on each chine [if it has them]. this strip may only need to be 1/2 to 1 inch high and the same width. If they'r made of Delrin ,aluminium or hardwood and carefully fastened with stainless counter sunk screws , carefully filling each hole drilled with resin the boat is made of before screwing, it may be enough to stop drift and be useful protecting the hull. Just a thought.
     
    Last edited: Jul 9, 2019
  7. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Senior Member

    You seem to be describing what is often called 'V hull waggle', which is an oscillating steering motion that a V-hull boat makes at low speeds. I might have missed it, but what brand/model boat are we talking about?

    I had a 24˚ V-hull boat and it would 'waggle' something awful at no-wake speeds (4-5 kts).

    A dual prop drive may help . . . and also taking any slop out of the steering system may help . . . but I have found that it is something that one can get used to, as long as you do not try to correct the 'waggle' with over-steering.

    I do like the idea of adding something permanent of fairly minimal nature at the chines of the boat, towards the stern. As far as strapping something to the hull, I find that getting the standard stuff on a boat to work properly is often challenging enough, so why complicate matters with something that isn't actually designed to be there :)
     
  8. John Shepherd
    Joined: Jul 2019
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    Location: UK

    John Shepherd Junior Member

    Again thank you. Good idea Trip, but I don't want to permanently add anything. And yes tpenfield, that's exactly right. There's usually a very clear difference between slow river cruising and faster estuary or coastal cruising so I figured that something temporary would aid the boat. As I say above, many fast planing fishers have a small keel to solve this problem, and I just figure it would easyish to try and see what happens. It would have to be removed prior to trailer recovery and of course added post launch so an easy on-the-water removable solution is a must. It maybe that the strap can contain two semi bilge keels to save grounding but that would just add the work and complexity. I'll have a think. And yes, a duo prop does go quite some way to help the problem. The boats is question at the moment are a Bayliner 245 or a Sea Ray 215. Neither of which have a duo pop :(
     
  9. alan craig
    Joined: Jul 2012
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    Location: s.e. england

    alan craig Senior Member

    Ballast tank and pump. Fill it with water on the river, empty it when planing. Some RIBs do this automatically; they flood and empty through holes in the transom.
     
  10. John Shepherd
    Joined: Jul 2019
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    Location: UK

    John Shepherd Junior Member

    Yes, that's a fair point Alan. I guess these are all possibilities. However, I'm not sure that would have the desired effect on the 'wandering issue'.
     
  11. The Q
    Joined: Feb 2014
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    Location: Norfolk, UK

    The Q Senior Member

    The Norfolk Wherry had a removable keel, held on normally by a pair of chains each end of the wherry.. This was an almost full length keel that JUST floated. and it normally lived under the boat. but if the Wherry had to go into shallow waters , it was dragged out from underneath and left somewhere. Note a Wherry was normally manned by just by a crew of 2. so it can't have been that difficult.
    Here is a picture of the last trading Wherrie' tn_L1020383[1].jpg s new steel keel being fitted to prevent Hogging..It's roughly the same size as the old removeable keel
     
  12. John Shepherd
    Joined: Jul 2019
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    Location: UK

    John Shepherd Junior Member

    Thanks the Q.. and great to know and very enlightening. Perhaps this means I'm not quite as mad as I thought.
     
  13. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    If your boat happens to trim by the bow (bow is down) it can make boat very helm sensitive and lead to 'over-steering' and 'wandering' - extremely easy to do with a 'directed thrust' system like o/b sterndrive, jets, etc.
    The ballast tank idea works but test it out first by going slow and having a few people (3-5) move from bow to stern & see how it responds. Quite often some stern trim is best.
     
  14. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    Another idea to consider is a removable transom hung rudder. This rudder would be used to steer the boat at low speeds only. At higher speeds, the rudder could be removed or retracted. The reasoning behind this idea is that the crazy steering of a "V" bottom planing powerboat (while not planing) is caused by turbulent flow aft the transom. The rudder that the boat is equipped with (if it's an inboard) is quite adequate for normal operating speeds which are all in the planing mode. Once off the planing, the poor little rudder (or outboard leg) just isn't big enough to cope. A sailboat rudder which extends past the bottom of the boat will get cleaner flow and will have much more area (maybe three to four times as much). This will give it far more authority at low speeds. Just keep in mind that only the rudder area beneath the bottom of the boat counts. The rudder does not have to be anywhere near the center line of the transom and may actually be more effective if it isn't.
     

  15. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    Yes, I have seen twin swing-down rudders on a 21' boat. I think the guy got them off a small dinghy. Just make sure the blades are 'up' if going astern at any speed.
     
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