Why aren't offshore tunnel hulls using forward wings to control bow lift?

Discussion in 'Boat Design' started by FranklinRatliff, Mar 28, 2012.

  1. BMcF
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    BMcF Senior Member

    The trimmable canards, you mean? Of course they are. What suggested to you that I 'hadn't noticed' or thought otherwise? Nothing I posted, that's certain.

    Have a nice day.:D
     
  2. FranklinRatliff

    FranklinRatliff Previous Member

    No, I meant the FULL WIDTH WING at the bow between the sponsons. And it's not "trimmed", it's DEFLECTED.
     
  3. powerabout
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    powerabout Senior Member

    Bow lift from water,air or drive train?
     
  4. BMcF
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    BMcF Senior Member

    Exactly.;)
     
  5. FranklinRatliff

    FranklinRatliff Previous Member

    Tunnel

    Lift from the ginormous f**king air trap under the boat. You know, the thing V-hulls DON`T have and so DON`T blowover?
     
  6. FranklinRatliff

    FranklinRatliff Previous Member

    Two reasons the front WING is not "trimmed." (A) it doesn't have trim tabs in the first place and (B) the ratio of foot pedal movement to wing deflection remains constant.
     
  7. BMcF
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    BMcF Senior Member

    By 'trimmed' or 'trimmable' I meant 'change in angle of incidence' and of the entire canard, of course. In 'other' vessel types where canards are employed, they are either all-moveable or will be fixed in place with a trailing edge flap, 15-20% chord. And controlled hydraulically.

    A different application of canards for pitch control, of course, but the terminology is similar, as one would expect it would be.
     
  8. Don H
    Joined: Apr 2012
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    Don H Junior Member

    Franklin, I think the simple answer to your question is they are not allowed to use wings. I am assuming the American Power Boat Association has pretty much the same rules as the Australian Power Boat Association and they govern racing in the US.
    From the rule book over here: dated February 2012.

    1407.8 and 1407.9 are the 2 relevant sections.

    Class 1 is offshore racing

    1407 WINGS - A wing is defined as a device above the deck that has a downward plus or minus 60-degree lower
    surface with an area in excess of 0.1 sq metres.
    1407.1 The use of any wing, whether for lift, down force or stabilisation is permitted only on Class 1 boats, provided
    that it is fitted to good standards or workmanship.
    1407.2 However, the following rules apply:
    1. The width of the wing cannot be more than 1.5 times the width of the hull for single hull craft and more
    than the width of the boat for multi hulls.
    2. The wing must be strong enough to bear a man’s weight (100 kg) at all points on it up to 1.2m from the
    ends.
    3. The wing should be fixed to the hull at least at four points in groups of two, spaced no less then 1.8m
    apart with steel bolts of a diameter of at least 14mm.
    1407.3 The use of shock absorbers that work under compression only is recommended.
    1407.4 A section smaller than that of the bolts must not exist at any point in the support.
    1407.5 A suitable transverse arrangement must be provided to make the fixing of the quadrilateral hyper-static.
    1407.6 Loss of a wing means disqualification from the race concerned & reuse of the wing is subject to technical
    documentary evidence that structural strengthening has been carried out.
    1407.7 The driver is entitled to decide whether or not to use a wing in case of each individual race, but the existence of
    the wing must be noted on the Measurement Certificate and the fitting procedure must be checked by the
    Measurer.
    1407.8 The wing must not be ahead of the crew or of the centre of gravity of the boat.
    1407.9 No trimable aerodynamic surfaces are allowed on the wing.

    The rules makers obviously don’t see a safety advantage of having a wing at the front of a Tunnel.
    Many years ago I raced tunnel hulls (cicuit tunnel hulls not offshore but many of the traits are the same) and I would agree with them I don’t believe a wing on a tunnel will have anywhere near the same effect as on a hydro. The 2 boat types are very different. The hydro is reasonably stable, it runs on 3 points (sponson rear on both sides and the prop). Its sponsons don’t travel the full boat length so the air compression between the sponsons only supports the front section of the boat. The rear is lifted by the negative trim from the propshaft.
    The trimmable canard between the sponsons doesn’t act like a foil on the front of an F1 car. It does provide some down force at speed but its real function is to cut off/ reduce the air supply between the sponsons and therefore reduce lift if the bow starts to climb.
    The tunnel hull has sponsons that travel the full length of the boat. The engines have positive trim and during a race you generally have the trim almost all the way out to get as much air underneath and lift as you can. Rougher conditions mean that there is also often water ballast at the bow to help keep the front down.
    The tunnel hull is very much a balancing act between the boat weight and how much air and lift you can get and it all pivots at the stern. When the tunnel is about to become a skyrocket there is a calm feeling where the normal vibrations felt through the boat get much less. This is the last chance to save it but it happens very quickly. The only way to stop it is to release the air under the boat. A wing would have to be enormous and almost point straight up to stop the boat from taking off. Turning the steering wheel hard to tilt the boat and let some air out can help on some occasions.
    Realisticaly though when you are in the boat this happens all the time and you never believe it will go all the way until it does.
    The boat in the video was already on the edge and that last wave that was a little bigger was enough to kick it past equilibrium and the engines just drove through under the boat.
    If there were huge vents between the sponsons to the upper deck, a quick release mechanism and a automatic angle sense to let the air out maybe this could have an application but I personally don’t think a wing would help even if you could operate it quick enough.

    Thanks Don
     
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  9. tunnels

    tunnels Previous Member

    Now thats what i call a really good answer to a seemingly simple question !!! but i could be wrong mind you !!:confused:
     
  10. yipster
    Joined: Oct 2002
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    yipster designer

    ya, specially when rules rule out wings on wingboats :D
    but yes most probably thats the correct answer
    do like the idea of venting lift, sorta like the M163 did
     
  11. FranklinRatliff

    FranklinRatliff Previous Member

    Thanks, Don! I was beginning to wonder whether I would ever get an informed and thoughtful answer. It seems to me the idea of large vent ports on the tunnel that could be opened in an emergency is something that should be investigated.
     

  12. Cawley
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    Cawley Junior Member

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