Spi + planing hull = ?

It'd be interesting to see a planing cat despite the fact that its a displacement boat.

Just exactly what is a planing wave piercing cat?
Can you tell us the boat models that were discussed???

Hi MauganH17,

Just to clarify, by "planing" hull I was referring to cats with flat bottom hulls like the Flyer A-cat which tend to jump over waves (also called "slappers" by some) vs "plowing" hulls which tend to more smoothly cut through the waves with rounder or v-shaped bottoms. I think everyone agrees all cats are primarily displacement boats with brief periods of planing caused by dynamic lift. I didn't mean that flat bottomed hull designs truely plane and that others don't and are displacement only. See discussion in prior posts under "Singlehanded Cat Sailing"...

Jerry

We realy should be starting to descriminate between different types of wave piercers (I dislike that description as well by the way.) We have several shapes right now after the Flyer introduced the concept. And the Flyer hull is different from teh FX-one which is different from the Bimare shapes which in turn can not be compared to that of the Blade. Some designers try to design "wave piercer hulls" by reducing bouyance fore and aft in the hull. Others by moveing this bouyancy away from the extremeties towards the centre under the main beam. And another implements this by only redistributing the bouyancy in the vertical direction while keeping the destribution in the horizontal sense unchanged. The different paths lead to the boats behaving differently under certain conditions. There is even a difference between the Hobie Fox and the Hobie FX-one in my personal experience. Therefor I don't think it can be stated that :"spi + planing wave piercing hulls don't mix!". It dependent on the design path followed.

The same must be set about displacement boats however. An Inter-18 is different from a Nacra F18 in this respect as well despite the fact that neither are regarded as "Wave piercers".

My questions are:

1) Has anyone else seen this? Cat and windspeed?
2) Has anyone seen this on cats with "plowing" hulls? Cat and windspeed?

No further comment on these points, I'm too involved.

3) Why does this happen to "planing" and not to "plowing" hulls?

It can to happen to both depending on the individual design of the boat.

4) If others have observed this, how is it influenced by boat weight and hull length (and why) - ie, would the same phenomenon be seen on A-cats, FXOne, and planing F16's such as Stealth/Blade (but not seen on I17 and T4.9)?

In your list of examples you have actually listed boats under "don't" that do and visa versa

Wouter

Wouter,

Thanks for your input. A few clarifications:

Can we agree on terms?
1)plower = cutter and planer = hopper
2)we don't mean plane as true planing or plow as displacement only
3)most cats share both of these characteristic depending on many factors including sailor weight position but some cats due to hull design show one of these characteristics to a greater degree much of the time

I had said:
"4) If others have observed this, how is it influenced by boat weight and hull length (and why) - ie, would the same phenomenon be seen on A-cats, FXOne, and planing F16's such as Stealth/Blade (but not seen on I17 and T4.9)?"

And you replied:
"In your list of examples you have actually listed boats under "don't" that do and visa versa"

I'm assuming you're referring to which boats are plowers/cutter vs planers/hoppers?

But in an earlier post "Single Handed Cat Sailing" you had said:
"The cutters more smooth and silent. The Taipan is a cutter and I believe the I-17 is so as well. The FX-one, Stealth F16 and Blade F16 are more of a hopper ... With respect to F16's ; Taipan 4.9/F16 is definately a cutter, Blade F16 and Stealth F16 are planers."

I had thought I was classifying the boats as you did; did I misunderstand you?

One of the reasons I raised the original question of spi + planing hull is related to another comment you made during the same post:

"With regard to the term planing. No cat planes fully and probably never will. It is indeed more like "having a (small) portion of its weight carried by dynamic forces created on the hull. I personally believe that such surfaces allow you to drive the boat harder without picthpoling and that explains more of the (possible) speed increases than the actual "plaining"."

So I had thought that a cat with planing hulls would be more resistant to pitchpoling and not less so while flying a spi and driving it hard. Yet the experience of one cat sailor goes against this. Which brings up a related question: how much of the pitchpoling characteristic of any hull design is due to boat setup/tuning? You and others have showed previously how changing the tuning of a boat can dramatically change sailing characteristics (ie, in reference to BroBru's I17). How much of this one cat sailor's experience might have been due to the boat he was sailing not being tuned well for the challenging conditions - and if so, what can one change on a cat to allow it to be driven hard off the wind cat rigged or spi that would help it avoid pitchpoling?

Speaking of tuning, one unrealted question: when you sail a cat such as a T4.9 or I17 cat rigged vs sloop vs spi, is it generally necessary to adjust standing rigging (ie, mast rake) or otherwise retune the boat for each configuration in order to allow it to sail properly (ie, balanced helm, pitchpole resistance)?

Thanks for the great input,

Jerry

Mast rake can have a large effect on stuffing. For hull shape, boats with more bouyancy forward are generally harder to stuff.

RBJ wrote

"4) If others have observed this, how is it influenced by boat weight and hull length (and why) - ie, would the same phenomenon be seen on A-cats, FXOne, and planing F16's such as Stealth/Blade (but not seen on I17 and T4.9)?"

And you replied:
"In your list of examples you have actually listed boats under "don't" that do and visa versa"

I'm assuming you're referring to which boats are plowers/cutter vs planers/hoppers?

No I'm not. I'm refering to diving under spi or remaining relatively stabil. Thus answering the original point of your post.

I all dependent on the hulls and also tuning setup. But I know hullshapes that most of the sailors call wave piercing that confirm the comment that you heard from an experienced racer and I also know a wave piercer hull that doesn't. Therefor the link between wavepiercer lable and diving under spi is not a good one.

This is mostly the result of an explosions of flyer copies which are all called wavepiercers but may be very different in behaviour just the same.

>>I had thought I was classifying the boats as you did; did I misunderstand you?

I was comment on the wavepiercer and spi don't mix; I wasn't at all refering to planing or plowing (or which other synonimes are used for this)

>>>One of the reasons I raised the original question of spi + planing hull is related to another comment you made during the same post:

"With regard to the term planing. No cat planes fully and probably never will. It is indeed more like "having a (small) portion of its weight carried by dynamic forces created on the hull. I personally believe that such surfaces allow you to drive the boat harder without picthpoling and that explains more of the (possible) speed increases than the actual "plaining"."

So I had thought that a cat with planing hulls would be more resistant to pitchpoling and not less so while flying a spi and driving it hard. Yet the experience of one cat sailor goes against this.

I think I have an idea on which boat the sailor making the comment has sailed but I can not comment on specific boat types in this manner in public.

I'll repeat what I stated earlier I know of "wavepiercers' doing well under spi and of wavepiercer not doing well. Visa Versa for "plowers" and spi. Therefor I think the comment made by the sailor is type specific and not "wave piercer" specific.

Of course I still think wave piercer is by now a useless term. It has been highjacket by several producers who make cosmetic changes to their boat to make it look like one but in all honesty don't understand what is really going on with the orginal wavepiercers. Others however do know and here the boats are better behaved.

>>Which brings up a related question: how much of the pitchpoling characteristic of any hull design is due to boat setup/tuning?

Mast rake can be important in the ease in which you initiate a dive, however hull shape determines whether this ends in a pitchpole or not. Therefor I would answer your question with tuning is not very important in pitchpoling and you can't trim it out of the boats without trimming away power or efficiency.

Fast and efficient boats are the ones that allow a boat to recover fully and with ease when it finds itself in a dive. The better the recovery the more powered up a boat can be trimmed and more to the edge you can sail it. Having said this I also know of a boat that can be sailed right up to its edge under full power without much diving or even bow down attitude BUT that will disappear from under you when you step over the edge. It is superior to others all the way up to the edge but you pay for it by having to learn the exact location of its limit.

This may not be the answers you are looking but this setup is a multivariable equation and simple rule often don't do it justice.

>>You and others have showed previously how changing the tuning of a boat can dramatically change sailing characteristics (ie, in reference to BroBru's I17). How much of this one cat sailor's experience might have been due to the boat he was sailing not being tuned well for the challenging conditions - and if so, what can one change on a cat to allow it to be driven hard off the wind cat rigged or spi that would help it avoid pitchpoling?

In general flying a spi on a catamaran will make it less dive sensitive. Quite a number of crews overhere pull spis in big wind not because of performance but because they feel they have a better controlled boat with it. I share this experience. It is weird to see a boat being actually worse off. I know the Dart 18 didn't take well to the spi. The only reason I can think of that would cause a cat to dislike a spi is that a hull doesn't have sufficient bouyancy in the bow and/or stern in relation to the leverage of the rig. I know some builders tried to imitate the wavepiercer concept by remove bouyancy at both ends without changing much else in the hull shape. I would look at these designs first if I had to name designs that could suffers under spi.

>>>Speaking of tuning, one unrealted question: when you sail a cat such as a T4.9 or I17 cat rigged vs sloop vs spi, is it generally necessary to adjust standing rigging (ie, mast rake) or otherwise retune the boat for each configuration in order to allow it to sail properly (ie, balanced helm, pitchpole resistance)?

I personally just trimmed the boat to an good average between modes and leave it like that. However, this does mean you can get some extra out of the rig by retrimming it when you are sure in which your are going to sail. I didn't really experience much problem with helm or pitchpole resistance. You know which boats I sailed and none appeared to be very sensitive to changes in setup. All cats with spi have leehelm, however I don't think this is a bad thing. After all the safety zone for sailing under spinnaker is to your lee and not to your luff as is the case when going upwind. It may not be excessive but that is logical.

Thanks for the great input,

Jerry

Wouter,

As usual, thanks for an extraordinary and very clear reply. I've read your comments previously that all wave piercing hulls are not created equal, but didn't make the connection to this specific behavior under spi.

What has become abundantly clear after getting great input from you and others is that to properly evaluate a cat it is really necessary to understand it's sailing characteristics (either in person or via experiences from others who you trust) for each possible mode (ie, cat rigged, sloop, spi, and sloop/spi), with each mode sailed under a very wide range of wind and wave conditions. So in this regard, even the usual good advice often given of "sail each cat once before you buy a new one" should be taken with a grain of salt since you might get a very incomplete understanding from a limited test sail under only one sail plan in non-stress test conditions. I don't like to be surprised!

I am so impressed with the quality of contributors to this forum and the enthusiasm with which everyone shares their experiences, expertise, and ideas. Only in this kind of forum would it have been possible to hear from one experienced sailor "this is what I observed" and get an insightful analysis from another "this is why he may have observed that".

Guys, what can I say but thank-you!

Jerry

Going back to the original question.

My first thought would be that the spin pole is too short on the boat that is burying.

Next I would look at mast rake (WAG 0 to 1 ft aft) and the look for water in the hulls.

Finally I would try to take both boats side by side and if one was still burying, I would swap spins to see if that was it.

The torque from the spin in winds over 10 knots is pretty big in comparison to the torque from the bouyancy at the bows for boat under ~20 ft. So, in general the spin is set to lift the bows. The longer the spin pole, the qreater the lever arm to torque the bows up and the greater the percentage of the force of the spin force that goes into lift.

This even works on boat that have no bows like Waves.

My $0.02's

Carl,

Great points.

Regarding the spi lifting the bows for boats under ~20 ft and 10+ kts: is the lifting torque influenced by spi tack sheet trim? If you trim this do you do it only for power/efficiency related to point of sail or do you do it to influence bow lift and associated boat handling characteristics?

Also, from what I understand, on pole-end snuffer systems you usually can't adjust tack sheet trim at all since the spi tack is usually shackled to the pole end; also on mid-pole snuffer systems using a single halyard to set spi head/tack you can't trim spi tack independently of spi head. What kind of snuffer do you use and do you ever concern yourself with trimming the spi tack?

Finally, at the risk of showing my ignorance, what's "WAG 0 to 1 ft aft"?

Jerry

Hi Jerry,
Don't get too carried with the technical information you get on this forum. There are some who speak loudly and don't know what they are talking about. They have never built a boat and never done scientific studies. Never put instruments on a beach cat and taken measurements upon which to base sound conclusions.
The man from Texas is right. If a spinnaker makes a boat dig its bow, the pole is too short. Aluminum tubing comes in 12ft lengths. Therefore many spin poles are 12ft long. It doesn't matter if that is the correct length pole for the boat or not; it is the length that is readily available so that is what is sold/used. A spinnaker that lifts the bows flies from a pole that is 45% to 50% of the mast height. A spinnaker flying in this mechanical arrangement will lift the bow no matter what the bow shape. The flying spinnaker unloads the bow no mtter what the bow shape.
"All boats that fly spinnakers have lee helm". Only boat designs that place the daggerboard in the classical position, approximately at the shroud chainplate, have lee helm with the spinnaker up. This is a system design that has ignored the spinnaker during the design phase of the boat development and the designer/manufacturer expects the sailing public to put up with it. There is a sail/boat design system that does take this CE migration into account. The design system is called "shared lift" and it is incorporated into ARC products. It has to do with shifting the board location forward so that the CE with spin up cannot get in front of the board. Then down sizing the board and up sizing the rudder so that the shared lift between the board and rudder is in the correct effective location for sailing the boat as sloop.
Good Sailing,
Bill

Bill,

Thanks for your comments. I understand there are differences in opinion on many issues but I have leaned from and respect the views of the prior posters (as well as your many insightful posts). I'd like to discuss any differences in opionion constructively.

I'll look into the mast height vs spi pole lengths to see if this contributed to the problem. I had actually thought they were fairly comparable but not sure of this. Your point regarding the moveable CE and how this can be address with a "shared lift" approach sounds innovative. The comparison I mentioned was between conventional daggerboard catamarans. But you do raise a related question: the majority of cats being sailed don't attempt to compensate for a spi induced forward movement of the CE; in fact, going downwind they usually raise their daggerboards moving the CLR even further aft in relation to forward moving CE.

Two questions:
1) Althogh they have some lee helm as a result I've not heard spi sailors complain about this so why is it a problem?
2) As catamarans sail fast downwind and are headed by their own apparent wind does their "spi migrated" CE shift aft somewhat as a result reducing the effect on lee helm? I've read on windsurfers in high apparent wind conditions and/or gusts the sail shape can change moving the CE aft even on their battened sails.

Jerry

Bill,

What instruments can you/have you put on a beach cat. How well do they work.

Gareth

Hi Jerry,
1)Cat sailors don't complain about lee helm with spinnakers up for two reasons. One is that there is nothing they can do about it; they have already bought their boat. Two is the other boats have the same problem so live with it.
Other examples of this attitude: H16s tack so poorly that the time and distance lost due to tacking usually outweighs the advantage of a new tack, so why tack? Who complains? It is the same for everybody in a H16 race, so what the heck.
H16s pitchpole easily on a reach so you can't be too aggressive and drive the boat hard in a breeze or you will pitchpole. Who complains? It is the same for everybody in a H16 race, so what the heck.
I see nothing but praise for the H16 on this forum. In West Palm Beach, Florida two sailors have lost their lives because of the unsafe characteristics, easy pitchpole tendency, of the H16 design. It is the same for everyone sailing a H16 so, what the heck.
2) With spinnaker up and sailing downwind, a given boat design sails to a constant relative wind angle depending on the wind strength. The direction of the boat may change in the puffs but the sailor tries to hold relative wind angle constant at max VMG downwind. If relative wind angle is held constant, then sail trim is held constant and CE does not move around once the sails are set and the boat is up to speed. When the CE goes in front of the daggerboard, you've got lee helm. So what, it is the same for everybody, what the heck.
Bill

I've kept my mouth shut for so long on this...

but Bill, you just can't help but take cheap shots at other boat designs can you?

EVERY post of your has a smart-assed remark about how such-and-such design blows goats compared to the ARC. While this may be true, is it necessary to sit there and talk sh*t about every catamaran under the sun? Its exactly like a politician who wont stop running a negative attack campaign. Frankly I'm sick of it. I really respect you for what you've done for our sport, but I'm seriously considering writing a script that removes your comments from everythread (on my end, don't worry Rick) just so I don't feel dirty after I read them.

Hi Gareth,
The instrumentation that I use for testing is made up of a compass and speedometer and slip angle measurement. I also carry a windspeed instrument. Frequently during a test the boat is turned head to wind and the windspeed and direction are recorded. The data is usually recorded on a pocket tape recorder so comments and special circumstances are noted in the data.
Bill

Hey MauganH17,

Chill out! This is a forum. Everyone gets his say. We listen to you right. I enjoy Bill's posts. I actually learn something on here when he speaks. Come to Round the Island next year in Ft. Walton beach and check out some of Bill's handy work. I believe last year he and his crew ( there were two I think ) were triple trapped on the downwind run at about 25 knots.

Happy Sailing

Tom

ps. Seems to me he is just stating some facts about the ole H16 that everyone pretty much knows.

Bill,
What is 'slip angle measurement' ?
How is it calculated or measured?
Thanks,
Chris

I think what Maugan is saying is that you don't have to tell a man his wife is ugly, even if it is a "fact."

I'm calm, I just "speak" (type) whats on my mind. I like Mary's analogy though, made me chuckle.

Perhaps Maugan was a bit strong...but the manufacturer and designer bashing is wearing on me too. If everybody else is so bad why do they sell so many boats? Bill, I don't think anyone doubts that you have designed some great boats but there are a lot of boats out there designed by other smart people too.

>>The instrumentation that I use for testing is made up of a compass and speedometer and slip angle measurement. I also carry a windspeed instrument.

And I thought your were talking about gyroscopes, GPS units and stress sensors. Everybody carries a compass on board and speedometers are outdated. Just use a GPS unit with tracking ability and make sure there is no current on the body of water you're sailing on. Having a reference boat around with reference crew helps a lot as well.

Talking about GPS tracking here is one from my personal archive. Note how the top speed (30 km/u=16 knots) of the sloop rigged craft is reached on ALL courses !

But then again I'm not a real designer.

Wouter

Hi Chris,
Slip angle is the angle between the boat centerline and the path of the boat through the water. It is simply a weather vane that runs in the water and the base is clamped to the boat. The vane is connected to a pointer just above the clamp/bracket that indicates the direction of the vane in the water as the boat sails. The difference in the vane indicated direction and boat centerline is the slip angle.
I have done alot of sailing with instruments on my boats because I don't have another boat to sail against so I sail against the instruments. This has helped me develope boats that are the fastest US Sailing has on record and cost 1/15th as much as a Formula 40 boat for example.
Bill

Hi Magee,
I'm only stating facts,not rhetoric. If you don't like them, I'm sorry. I wrote the comments that you don't like in the style I did for emphasis. I think boat safety is NUMBER 1 in order of importance. That is why the SC/ARC boats are the shape they are, elliptical hull cross section shape. That is why all SC/ARC boats come with a righting system from the factory. As soon as you leave the shore on a beach cat and the water is over your head, you are "at risk" and your beach cat put you there. Your beach cat better be able to take you out of an "at risk" situation, like a turn over.
SAFETY, SAFETY, SAFETY is NUMBER 1 in order of importance in any boat design.
And by the way, Magee, some day all beach cats with spinnakers will have the daggerboards close behind the main beam or maybe just in front of the main beam. It is just going to take a while for them to get there.
Some day all beach cats will have self tacking jibs. It is just going to take a while for them to get there.
Some day all beach cats will come from the factory with righting systems. It is just going to take a while for them to get there.
Good Sailing,
Bill

You are right, Wouter, you are not a real designer. You are a buyer and a user and a talk abouter. Back in the 1970s and early 1980s when I was doing my basic beach cat design/study work, there were no GPSs. What would you suggest I do; wait until the 1990s to gain understanding about the design and performance of beach cats using a GPS? The last clean sheet design I did on a beach cat was 1979, the RC27, winner of the Bol De Or race in 1989.
Dream on, Wouter.
Bill

Bill,

What have I done to deserve :"Wouter, you are not a real designer. You are a buyer and a user and a talk abouter" ?

Apparently I'm also a GPS user taking measurements upon which to base sound conclusions IN 2003 !

Not 1978.

And who exactly were you refering to in :

"... who speak loudly and don't know what they are talking about. They have never built a boat and never done scientific studies. Never put instruments on a beach cat and taken measurements upon which to base sound conclusions ..."

I get the funny feeling that that "who" is somebody I know personally.

Wouter

Hello to EVERYONE,

...just so you know,..I learn from ALL OF YOU!

...just so you know,.. diversity and different points of view is what drives innovation

..you all are just great,.....except for one ting, mon

...you should be packing up your boats to come sail down here....Rolex in St. Thomas is last week in March, 5 days later is BVI Regatta

...we can sail all day......

regards,
Bruce
St. Croix

ps; my next boat is a ARC 27,...I need something a little bigger down here

Man oh man. I love the islands. If I don't get a job with the FAA, My Wife and I are just going to sell everything and move there. I'll figure out where to work once I get there.

Hi Bill,

What you (and others) said about lee helm under spi (without CLR correction) sounds both obvious and right and is concordant with many peoples experience; however, I still wonder if it's as simple as you say because today when I discussed this very issue with an experienced I20 racer he SWORE to me that he has a nearly neutral helm under spi (as well as upwind as a sloop).

Why?

Could it be that when one raises their boards off the wind and significantly reduces the magnitude of their CLR the migration of the CE becomes a non-issue (ie, they are not seeing lee helm because they are side-slipping downwind on their broad reach)? This effect might be pronounced on cats with flat bottomed (semi planing) hulls and not observed on cats with deeper hulls - hence different sailors observe different amounts of lee helm. Also, at speed, couldn't the rudder/aft hull be generating sufficient lift to compensate for some forward sail CE migration (when their boards are raised)? Finally, wouldn't the very presence of a spi augment the mainsail's lift (ie, slot effect) effectively moving the aggregate CE back somewhat? (I hope my inexperience and/or naivete isn't showing too badly...).

Who else out there has spi experience on an I20: do you see lee or neutral helm? Anyone else out there on any other (non ARC/SC) spi cats ever see neutral helm?

Jerry