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May 23, 2014, 08:03 PM
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Dick L.'s Avatar
Ted - just a thought about collisions with reverse bows.

While I see your point, it is also possible the bow of the "striking" boat could be pushed down and under the hull of the "struck" boat - possible reducing or eliminating any hull puncture. That said, it is ALSO possible instead of a punched hole the height of the bow, the loss of a rudder of the "struck" boat might be possible if that boat keeps sailing up and over the boat with the reverse bow.

In either case, I would think trying to design for this situation (poor seamanship/knowledge of "right-of-way") is not a logical design effort - but rather an outcome with a conclusion of a more stable boat.
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May 24, 2014, 12:50 PM
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Quote:
Originally Posted by Dick L.

In either case, I would think trying to design for this situation (poor seamanship/knowledge of "right-of-way") is not a logical design effort - but rather an outcome with a conclusion of a more stable boat.
You can call it "poor seamanship/knowledge of right of way" if you wish but the fact is that in RC racing due to distance, line of site, and an occasional misjudged dip, collisions will happen, certainly most are not done on purpose or stupidity, but stuff happens. We already have rules in many classes that have rules in place to avoid damage in the event of a collision, IOM for instance.

I am confused by your last comment...are you saying a wave piercing bow is more stable? If so how do you know that?
May 24, 2014, 09:28 PM
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Dick L.'s Avatar
Original point was perhaps (theory) a buried bow would slide "under" the other boat, rather than punch a hole........ i.e. provide a "ramp" like a door wedge. As for stability, if it wasn't, do you really think so many hulls in the big world would be following the design concept?

I don't dispute your first paragraph at all, BTW.
May 24, 2014, 10:44 PM
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Quote:
Originally Posted by Dick L.
Original point was perhaps (theory) a buried bow would slide "under" the other boat, rather than punch a hole........ i.e. provide a "ramp" like a door wedge. As for stability, if it wasn't, do you really think so many hulls in the big world would be following the design concept?

I don't dispute your first paragraph at all, BTW.
Some things I wonder about when comparing full scale boats is not having moveable ballast ( a human in boats like A Cats or other small cats), or a chute to pull the bow up in bigger boats. Just not sure how to get enough buoyancy forward in an IOM.

Kind of like great big wide transoms like the Volvo boats, they are made to go down wind on a broad reach and plane on that great big fat flat run aft, won't work on an IOM at all these days.
May 25, 2014, 08:56 AM
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Dick L.'s Avatar
I agree
May 25, 2014, 12:37 PM
David Cook Victoria, BC Canada
Thread OP
Tumblehome forward increases buoyancy. Having a fine entry quickly turning into full sections forward is the best (in my opinion) compromise for a wide variety of conditions.
May 25, 2014, 08:57 PM
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Quote:
Originally Posted by PorkyPig
Tumblehome forward increases buoyancy. Having a fine entry quickly turning into full sections forward is the best (in my opinion) compromise for a wide variety of conditions.
Dave,
This is exactly what I was trying to do in Rhino's design. With a simple cut swept back on the bow section, I can easily make a WP front end on the hull.
May 26, 2014, 12:34 AM
NORTHLAND NEW ZEALAND
D design's Avatar
Seems there's a bit of confusion here about reverse bows. There are a few types of reverse bows. You have wave piercing bows, and you have water removing bows(what I like to call it). Wave piercing bows sail through the wave on and off the wind to reduce wave resistance on long narrow hulls. This is why it is usually seen on multi-hulls were they can get away with the narrow beam due to low displacement. Water removing bows do not go through the waves but go over the top. They are designed to quickly remove water that has come over the deck. Both types of bows significantly reduce aero drag. Wave piercing bows, however hard you try will never work well on an IOM due to an IOMs displacement. If you did achieve it your IOM will not track with the wind.
May 26, 2014, 04:38 AM
AUS 1941
coolmobility's Avatar
Also, wave piercing is not so much for efficiency but to decrease pitching for a more stable and comfortable ride for occupants. Like stabilisers on ocean liners, to decrease roll and pitch, there would be an energy and inertia loss. It takes power and inertia to penetrate a wave - IOMs are too light to power through a wave. I know what it was like paddling a narrow kayak out through surf, easy riding over rollers, but going though a breaker took me backwards to try and get forward momentum going again - really hard work.

Admittedly, the rig pitch-poling is not good for efficient power, a light boat will always ride over a wave, especially with a buoyant bow with volume. Just look at a Volvo 70, with its fine entry, smashing through waves and the whole boat shudders as it hits each wave. For an IOM this would be almost as bad on momentum as burying their nose - they'd just stop!

It's hard to be sure that big boat handling and model boat handling are the same as water density is not scaled but basically standard, so I could be very wrong, but I'd hate to try and sail my 25 footer through waves the way the maxi boats do! My 1,800kg, 7.62m long yacht would just stop and lose all momentum - if that scale decrease is the case, then extrapolate that and a 4kg, 1000mm hull should stop too.

Just my thoughts on this and I may be shut down by those who try it but I'll go with water shedding bow with a reasonably fine entry as a better option over trying to "piece" through waves. Besides, the stern will rise and lift over waves so hull won't stay level anyway.
Last edited by coolmobility; May 26, 2014 at 04:46 AM.
May 26, 2014, 05:24 PM
Registered User
Quote:
Originally Posted by D design
Seems there's a bit of confusion here about reverse bows. There are a few types of reverse bows. You have wave piercing bows, and you have water removing bows(what I like to call it). Wave piercing bows sail through the wave on and off the wind to reduce wave resistance on long narrow hulls. This is why it is usually seen on multi-hulls were they can get away with the narrow beam due to low displacement. Water removing bows do not go through the waves but go over the top. They are designed to quickly remove water that has come over the deck. Both types of bows significantly reduce aero drag. Wave piercing bows, however hard you try will never work well on an IOM due to an IOMs displacement. If you did achieve it your IOM will not track with the wind.
As Neil says, and I have also said previously, it is impossible to design a genuine WP bow and hull within the IOM rule. We know, we've tried. The minimum displacement requirement defeats it.

However, with the experience of the Panic, I disagree that there is a a hard and fast division between the way WP and WS (water shedding) bows act in waves. Interestingly, while there is not much difference in the volume of the Panic bow compared with the Britpop's below the waterline, their action through the water is greatly different. Though I guess the Panic's bow should properly be described as WS rather than WP, it still does knife through waves rather than rising to them, and as a result does pitch noticeably less than the Britpop.

I am with child to see how the Mk2, with refined shape and reduced volume, will perform. Hurry up Neil...
May 26, 2014, 06:42 PM
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ndeverell's Avatar

D2


Hi Guys

The big advantage we have noticed with the D2 bow shape is when the boat is heeled and sailing into a chop the waves don't knock the boat around compared to conventional boat with a hard cornered gunwale forward
This was the intention of the design and has proved to work well
in fact the more it heals the better it goes

added bonus has been downwind when the bow goes under the boat does not slow
so there is less pressure from the sails trying to flip the boat .

This is very noticeable when the boat is at speed down wind compared to when a gust hits the boat when it is moving slowly resulting with a flip out

We have also found big advantage in windy B rig conditions as the less wind age helps a lot with tacking and start line positioning

We are very happy how the D2 works with the above waterline shape and we are now designing a D4 looking at a better underwater shape!



cheers
Neil
May 27, 2014, 10:08 AM
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ToniGe23's Avatar
it's all well and good looking nice above deck and nice shapes below but is a BritPop beater!
May 27, 2014, 03:37 PM
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Crunchy Frog's Avatar
Neil,

What is the weight of a bare hull? And are you taking orders yet?
May 27, 2014, 07:02 PM
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ndeverell's Avatar
Quote:
Originally Posted by Crunchy Frog
Neil,

What is the weight of a bare hull? And are you taking orders yet?
You can order a boat through our website

http://www.halfmodelboats.co.nz/iomprice.php

Grand Prix boats need 300 gram correcter weights

cheers

Neil
May 28, 2014, 11:53 AM
Flying without a licence
FWAL's Avatar
Quote:
Originally Posted by ndeverell
You can order a boat through our website

http://www.halfmodelboats.co.nz/iomprice.php

Grand Prix boats need 300 gram correcter weights

cheers

Neil
I would guess to answer CF's question a bare hull would weigh around 580g based on the following:
Fin & bulb 2500g, lead corrector 300g, rig 300g, RMG winch 135g, LiPo 2S 1550 mAh 120g, rudder servo 35g, pot and sundry fittings 30g = 3420g + Hull 580g = 4kg
Last edited by FWAL; May 28, 2014 at 11:55 AM. Reason: LiPo correction


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