The Pitchpoling Myth

A gradient of 1 in 4 means that it requires 4 metres of length to produce a rise of 1 metre, whereas with 1 in 6 it takes 6 metres. So 1 in 6 is less steep. So for the same clearance it requires a less steep wave to reach the bridgedeck with the wider hull spacing

 

Transverse stability.

A handy sketch of transverse stability.
The sail is square and set from a yard.
The blue dot is the CP.
The moment originating from CP can be directly transferred onto the 'line of transverse stability' now.

 

and continuing the theme...

Move the yard to the drawn mast next.

Then make the sail a leg o' mutton mainsail.

That blue line originating from the CP can be transferred to deck level.

That blue line is the direction of the moment.

So if moment on that line is 500kg@ 20m, then it is 1000kg@ 10m.

But it is only in the direction of total force at the CP.

 

Got to confess I own a Stealth although I'm not sure I have enough experiance of big cats to comment. From a Stealth perspective the T foils are very very good at stabilising in pitch movement, certainly it makes their modest 16ft seem much longer. I have sailed with both ordinary rudders and T foils on the same boat and would say using the T foils are a step in the right direction in that all pitch movements are much dampened and thus allows the Gorilla on the back more time to do something about the impending splash.

There are several photo's of a Stealth getting deeper and deeper on the leeward hull, until the hull is almost fully submerged but almost horizontally uniform along the water line such is the power of the T foils to stabilise. There is a very good video on the Stealth Marine website which shows the T foils at work.

I think also the flat bottomed design of the boat also prevents the boat pitch poling as one normally has the Spinnaker up ( our spinnakers are now so flat as to be more hooter than spinnaker ) on the longest pole allowed which lifts the bow and lets the flat bottoms do there stuff.

These 16ft rocket ships which only weigh 100kgs all up really are very different than the cats generally talked about on this forum, if you can get a chance to hitch a ride on a F16 style cat then give them a go, they really are a great adrenaline rush with really good boat handling manners, ie you can do some really crazy fast sailing but still feel totally in control.

 

Stealth F16

Great comments! Thanks Wayne. Do you have any serious problems with weed on the t-foils?

 

OK Alan, so what you are saying is this? I was trying to imagine a more complicated picture.

Cheers

 

Surprisingly little as the T foil itself is a very rounded semi circular shape, only a direct wrap around the central rudder may pose a problem. To be honest the areas I have been sailing are pretty weed free so I may not have seen the worst possible conditions.

To sort of retiterate my previous statement, the T foils do " dampen " the pitch movement really well and its a rare occurance to see the Stealths pitchpole despite the very large area they sail with.

 

Yes, that's what I was saying. Your diagrams show it much better than my words did.

 

The Pitchpoling Myth

I am too impatient to wait for Richard Woods to make his conclusion, so I will make it for him....

The Pitchpoling Myth has been busted...and it has not been busted.

There are no golden rules. One rule will always affect another. I think we can all agree that yacht design is all about finding the right balance.

Now everyone can relax and get back to what they were doing.

bye

 

But, but but, I was waiting my chance to pontificate too - Oh well.... another thread prematurely wound down?....

 

Stoke it up Mas The fire fizzled out ages ago.

 

I havent found a myss to pitch my pole yet and the only boats that go upside down were caused by the "skipper"..... guns don't kill people the fool using it does - on that basis of anal ysis by the NRA, then people who capsize their boats should be given a gun?

 

extreme anal ysis, Mas.