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Keels and masts

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Created by sailorsilas A week ago, 13 Sep 2021
sailorsilas
15 posts
13 Sep 2021 12:25PM
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I saw somewhere some time ago some pics, or on YouTube, of boats with the different sail configurations eg sloop, cutter, slutter, solent etc. the side on pics showed the relationship of the mast with whatever type of rig to the keel. Whether the mast was more forward or back depending on the type of rig. Does anyone know where I can find pics of that as I've looked on google etc and can find nothing except generic type drawings.
Thanks

julesmoto
NSW, 269 posts
13 Sep 2021 4:19PM
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sailorsilas said..
I saw somewhere some time ago some pics, or on YouTube, of boats with the different sail configurations eg sloop, cutter, slutter, solent etc. the side on pics showed the relationship of the mast with whatever type of rig to the keel. Whether the mast was more forward or back depending on the type of rig. Does anyone know where I can find pics of that as I've looked on google etc and can find nothing except generic type drawings.
Thanks





Why are you wanting to know?
Each model of boat will have settled upon a particular keel placement v the rig and either it works properly or it doesn't which can be determined by sailing the boat or asking owners whether they experience severe weather helm or lee helm in any particular conditions ( or hard to control downwind performance).

john24
41 posts
13 Sep 2021 3:13PM
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The rigging doctor youtube channel has both videos on rig types and different keel designs. Can't remember if they discuss both in the same videos.

r13
NSW, 851 posts
13 Sep 2021 5:24PM
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The topic is termed "balance" of the combined rig and hull /keel / rudder design and governs the "lead" (% of Length of waterline) that the centre of effort (CE) of the total upwind sail plan must be in front of the centre of lateral resistance (CLR) of the combined hull, keel and rudder. Principles of Yacht Design (Larsson et al) 4th edition covers it in Chapter 8, 8 pages. The below link seems like it has most of this chapter but it may be from an earlier edition of the book - still all valid obviously - click through the various pages on the topic about 5 of them.

www.boatbuilding.xyz/ship-design/balance.html

The PoYD 4th edition summary recommendations are;

For long keel yachts - masthead sloops 12-16%, fractional rig sloops 10=14%, ketches 11-15%.

For fin-keel yachts - masthead sloops 5-9%, fractional rig sloops 2-6%.

The below link is a good summary from a sailmaker;

www.uksailmakers.com/news/easier-faster-sailing-when-balanced

I would expect that these rules of thumb might need to be varied for the more recent design full bow wide stern twin rudder hull shapes which are intended for suitable upwind speed but breakaway downwind speed - eg as per here;

www.sail-world.com/news/240929/Rolex-Fastnet-Race-Onboard-SWELL-Video

Be interesting to work out what the 3300 lead is but a quick search did not bring up any under profile drawings.

www.jeanneau.com/en-au/boats/sailboat/1-sun-fast/640-sun-fast-3300/

The JPK1080 is a similar design and the dwgs at the below links would enable the lead to be estimated.

sailboatdata.com/sailboat/jpk-1080

www.prime-time.fr/bateau.php

For downwind balance - reaching and broad reaching put up the biggest kite you can manage based on the course direction needed, keep the kite filled (but perfectly trimmed obviously with maximum luff roll before collapse as relevant) and dump the main if round-up seems imminent.............if round-up occurs and the course needs to be maintained set a smaller kite or drop it and 2 sail reach again............. running more square again biggest kite you can carry but obviously don't broach or chinese gybe...................get all crew well aft............





sailorsilas
15 posts
13 Sep 2021 7:10PM
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Thanks everyone, I know what the different configurations do but I'd like to find the pics as mentioned.

lydia
1404 posts
14 Sep 2021 3:58AM
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All about centre of effort and centre of lateral resistance
Match them and you need no helm so quicker.
But 95 % of drivers can't steer with no weight on the helm, therefore slow.
Etchells are a great example, the rudder is so crap you turn yourself inside out moving the mast butt and forestay length trying the trim out helm in different breeze strengths
The butt might get moved 50mm while the forestay length change 100mm and even boats from different builders will have different positions
But the issue is still the same, balance

Chris 249
NSW, 2689 posts
14 Sep 2021 8:15AM
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I think any racing boat designer these days will say that there's nothing wrong with having the CLR a touch aft of the CLE and therefore requiring a bit of angle on the helm. By giving the rudder a significant angle of attack, you can get the same amount of lift on it as if it was a bigger foil with greater skin drag and take a significant amount of the side loadfing off the keel and it ends up creating a faster boat.

There's an interesting analogy with longboard windsurfers, where you can easily balance the CLR and CLE so that there's no load on the fin. However, in practise it's better to load the fin with sideforce even though it's at the same angle of attack as the centreboard. It's hard to isolate fin loading from various other effects, but the idea that

lydia
1404 posts
14 Sep 2021 1:52PM
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Chris 249 said..
I think any racing boat designer these days will say that there's nothing wrong with having the CLR a touch aft of the CLE and therefore requiring a bit of angle on the helm. By giving the rudder a significant angle of attack, you can get the same amount of lift on it as if it was a bigger foil with greater skin drag and take a significant amount of the side loadfing off the keel and it ends up creating a faster boat.

There's an interesting analogy with longboard windsurfers, where you can easily balance the CLR and CLE so that there's no load on the fin. However, in practise it's better to load the fin with sideforce even though it's at the same angle of attack as the centreboard. It's hard to isolate fin loading from various other effects, but the idea that


That was early IMS days when kernel area was expensive and rudder area was cheap rating wise so the boat was set up get more lift off the rudder at the expense of speed.

Loading up a single fin is no different to going "bow down" with a high lift keel
More speed equals load equals more lift.

r13
NSW, 851 posts
14 Sep 2021 9:56PM
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Not sure what more "pics" you need sailorsilas. The links I provided have numerous technical drawings explaining it all. If it is wanted of the forum to find the exact link to what you saw before, but you cannot find now, then this might be a task too far.

Thanks Lydia there are numerous web articles as regards steering an Etchells fast - all of them involving minimal rudder action (which creates drag and less speed as you allude to) rather rig and sail trim. Have steered a few races on an E22 - way and above the best balanced yacht have ever steered.

As further potentially helpful responses;

The 4th ed of PoYD is dated 2014 reprinted 2016.

Interesting article on the topic here;

www.rsyc.org.uk/Uploads/Documents/Claughton%20HISWA%202013.pdf

I have done a very quick lead estimation of the JPK 1080 as below, based on the below technical drawing and data. The result is that the CE leads the CLR by around 3.3%. Of course this is an estimate based on the technical drawing and data - the designer would have the exact calculation.

So this is the lead of the CE in front of the CLR for the upright configuration of the rig. When the yacht is heeled under actual upwind sailing conditions the CE of the sailplan being moved to leeward of the hull in plan view will result in a turning moment into the wind - which needs to be counteracted by rudder action ie weather helm. The same issue applies to wide sterned yacht hull shapes - when heeled they create a turning moment into the wind.

So CE location of sail plans and CLR of hulls need to keep in mind heel impacts of the rig and the hull.




Jolene
1354 posts
14 Sep 2021 8:58PM
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I think sailorsilas was looking for a specific set of pictures. Not advice or lectures. Had to laugh at the first reply of "why are you wanting to know " what a ****ing wanker

sailorsilas
15 posts
15 Sep 2021 6:51AM
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Sorry, but it seems I wasn't too clear in what I asked so I'll try to simplify the request, but thanks for the all your responses though.
Here goes-
hmmm, not sure I can make it simpler, but different types of sail setups apparently have the keel in different places (in relation to the mast) on the boat so that the boat is balanced when sailing. What I'm looking for are pictures of the above - not explanations of how a boat behaves with the different types of sail setup. I want to see where the mast is in relation to the keel for a slutter as against a sloop etc as an example (presuming it's the same boat with different sail configurations if that make sense).
thanks

Chris 249
NSW, 2689 posts
15 Sep 2021 8:57AM
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Jolene said..
I think sailorsilas was looking for a specific set of pictures. Not advice or lectures. Had to laugh at the first reply of "why are you wanting to know " what a ****ing wanker


Yep, but this is the internet and discussions evolved. I had a fairly long look to try to find the illustration he was looking for with no success.

Chris 249
NSW, 2689 posts
15 Sep 2021 9:50AM
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sailorsilas said..
Sorry, but it seems I wasn't too clear in what I asked so I'll try to simplify the request, but thanks for the all your responses though.
Here goes-
hmmm, not sure I can make it simpler, but different types of sail setups apparently have the keel in different places (in relation to the mast) on the boat so that the boat is balanced when sailing. What I'm looking for are pictures of the above - not explanations of how a boat behaves with the different types of sail setup. I want to see where the mast is in relation to the keel for a slutter as against a sloop etc as an example (presuming it's the same boat with different sail configurations if that make sense).
thanks


I can't find pictures, but Juan Baader's "The Sailing Yacht" provides suggested leads (ie mast/keel positions) for different rigs. For a cruising sloop, he recommended 7-10%; for a yawl or ketch, 4 to 6%; for a schooner, 3 to 4%. Like Marchaj and Larsson and Eliasson, Baader then goes on to stress that these figures are subject to many other factors.

Out of interest, I checked up a few boats where the hull remains the same but the rig is moved to adjust for the rig. In the classic Swan 65 the ketch's mainmast is about 30cm forward of the sloop's. However, I think that the best Swan 65 "sloop" often used a cutter/slutter rig, as did many Australian boats in the same period due to the limitations of sailcloth and gear. To complicate matters, at least one Swan 65 ketch won (or came close to winning) the Swan World Cup in more modern times with the mizzen mast stepped, but no boom or sail on it.

The Swan 57 - same designers, same builders - apparently had the mainmast in the same position in both ketch and sloop version, but the ketch had a 2' shorter boom. The same occurred with, for example, the Arcadia 30 (I just picked that as it's the first example of a dual-rigged boat on Sailboat Data's alphabetical list); the well-regarded Alberg 37, and many other boats. Even in the classic boat era, designers like Fife, Watson and (I think) Herreshoff converted cutters into ketches by just cutting down the main boom and adding a mizzen.

The fact that designers like S&S didn't move the keel or rudder all the time whe they changed rigs indicates that anyone that it must be done, or even that it should be done, is probably ignoring many of the other factors involved. The discussion above about helm balance indicates just one of those factors.

Apologies if this is teaching you to suck eggs, but this is a forum and conversations diverge.

Chris 249
NSW, 2689 posts
15 Sep 2021 9:53AM
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Jolene said..
I think sailorsilas was looking for a specific set of pictures. Not advice or lectures. Had to laugh at the first reply of "why are you wanting to know " what a ****ing wanker


It was a reasonable question. Silas may have been wanting to know, for example, whether a particular ketch he was looking at would sail well even though the keel and rig were in the same position as a sloop version. He may have been wanting to know if a ketch he sailed had weather helm for any particular reason.

Chris 249
NSW, 2689 posts
15 Sep 2021 11:03AM
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If we're just talking about Etchells then yes, no helm may be quicker; my Eggshell days were long ago. But in other boats apart from early IMS boats, positive angle of attack on the rudder can be faster and that's still very current;

www.northsails.com/sailing/it/2020/01/span-squared

Mark Mills is quoted as saying in 2017 "In light airs you want more rake back to load up the rudders and give you some [rudder] angle, and as the breeze comes on you want to rake the rig forwards and reduce that to keep the rudder angle at 3-3.5 degrees." Similarly, guys like Olympic cat medallists also set their boats up for a slight angle of attack on the rudder, and that's not 'cause they are bad sailors.

There's no real reason why slightly increasing the angle of attack of a rudder, and therefore allowing it to develop lift, is a bad thing.

Kankama
NSW, 371 posts
15 Sep 2021 2:00PM
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I am not a fluid mechanics person but all of the boats I have raced have had weather helm. A little has always seemed fast but I race dinghies mostly.
I looked up some data on a NACA 0012 foil. At 0 angle of attack it has no lift and a Drag coefficient of 0.0092. At 4 degrees it has lift coefficient of 0.449 and a drag coefficient of 0.0108. The lift at 4 degrees is about 1/3 of the maximum lift of the foil. So by getting the foil at 4 degrees angle of attack you get a lot of lift (1/3 maximum from the rudder) for a very small drag penalty. Reynolds numbers could be a thing here but the CD vs angle of attack graph is pretty darn flat at low angles of attack. So loading up the rudder is almost free lift, reducing load on the keel which always has to act at a negative angle of attack. It is going to reduce leeway and reducing angle of attack on the keel will reduce its drag slightly, so a correct balance will allow you to go faster and make less leeway. I like NACA 0009 and 0012 foils. Good dependable foils that a guy like me can make. They seem to work well on my boats.

www.quora.com/Where-can-I-find-Naca-0012-airfoil-lift-and-drag-coefficient-data-in-a-downloadable-format

I would recommend the Bob Perry book on yacht design. It has some great sections on how he designs his monos. The chapter on rig selection and types would answer most of the OP's questions. Perry is a great read with fab insight into design. I am not a huge fan of all his boats, but reading the book is very instructive. Also the Ron Holland book is a great as well but with less design stuff in it.

PS Good article Chris - I didn't know most of the stuff in it.

r13
NSW, 851 posts
15 Sep 2021 6:04PM
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Tag team strikes again

Kankama
NSW, 371 posts
15 Sep 2021 6:43PM
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He must be a clever guy. I tend to agree with him, except at Christmas and birthdays. Unless we are racing the same boat, then we don't agree much at all!

r13
NSW, 851 posts
15 Sep 2021 10:18PM
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Kankama said..
He must be a clever guy. I tend to agree with him, except at Christmas and birthdays. Unless we are racing the same boat, then we don't agree much at all!


Goodo, same here, been sailing on and off with 2 brothers for ~55years starting in Manly Juniors of course......including a couple of Hobarts in a company owned (not my company, I was a graduate engineer feudal serf who could sail...) Farr11.6..........



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"Keels and masts" started by sailorsilas