Planing
Printed From: Yachts and Yachting Online
Category: General
Forum Name: Beginner questions
Forum Discription: Advice for those who are new to sailing
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=6652
Printed Date: 09 Aug 25 at 6:56pm
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: Planing
Posted By: ellistine
Subject: Planing
Date Posted: 20 Apr 10 at 1:08pm
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Daft question perhaps but how do you know when a boat is
planing? I initially thought it was when it started to hum but I now know that's more the result of a crap foil. Assuming 'quiet' foils what are the indications that boat has just start to plane? |
Replies:
Posted By: JimC
Date Posted: 20 Apr 10 at 3:31pm
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I think its one of those questions where the more you know about it the more difficult it is to come up with an answer! The older (maybe even wiser, but I doubt it) I get the less I think I understand the difference between planing and not planing. I don't think there's a hard and fast definition and I'm very sure there's not a single point at which a boat is or isn't planing. Its more a question of a range during which a boat is partially planing...
That doesn't help at all does it! Why do you want to know? |
Posted By: Matt Jackson
Date Posted: 20 Apr 10 at 4:11pm
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Thought I read an interesting definition in my Tasar manual years ago which was based on the position of the bow wave relative to the hull where (and this is where it gets a bit hazy) fully planing is when you overtake the bow wave. Sounds wrong when I re-read it. ------------- Laser 203001, Harrier (H+) 36 |
Posted By: ellistine
Date Posted: 20 Apr 10 at 4:14pm
Just trying to get to grips with some sail trim issues (jib sheet tension mostly) and from what I've been reading there's a distinction between sub-planing and planing. ------------- |
Posted By: JimC
Date Posted: 20 Apr 10 at 5:08pm
OK, for that then, what you need is to know what the author of the article regarded as sub planing speed! For a lot of people the point is where the wake goes smooth and you get a wake line from the chines meeting somewhere aft of the transom. A powerboat racer, for instance, would regard planing as being a speed so high that there are only a tiny handful of dinghies capable of reaching it: in his terms most dinghies never get out of a semi-planing mode... |
Posted By: ellistine
Date Posted: 20 Apr 10 at 5:19pm
That sounds logical. I'll have a look out for them. Thanks. ------------- |
Posted By: ColPrice2002
Date Posted: 21 Apr 10 at 9:40am
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Hi, If you remember (?) - a "displacement" hull has to push the water aside as it sails. There is a formula - max speed = 1.3 times square root of the waterline length. Note speed in knots, length in feet and 1.3 is a factor that changes depending on the hull shape in question. So if you have a 16 ft boat (say a Wayfarer - for easy math!), max displacement speed is 1.3 x 4 = 5.2 knots. In a heavy yacht, there is no way that you can go faster (unless surfing) so you would adjust the sail area to sail at 5.2 knots. A saining dinghy, however, can "climb" out of the water and skin on the water. At this point, the hull isn't trying to push water aside, so the drag force reduces significantly, and the boat will plane. In a small dinghy, the transition can be dramatic (bow lifts out of the water, accelerates, "clean" wake). Just before planing, the dinghy will be making large bow & stern waves. Often there will be a high bow wave - with spray - not solid. The exact details will vary depending on the hull sections. HTH |
Posted By: JimC
Date Posted: 21 Apr 10 at 10:04am
Its *much* more complicated than that!! Nothing special happens exactly at the point of the Froudes law calculation, but this is the beginner's topic. |
Posted By: ham4sand
Date Posted: 21 Apr 10 at 2:52pm
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there is something about it in highperformance sailing....not sure the exact details as havent got it with me but i think its something to do with passing the quarter-wave or something like that ------------- John Hamilton cherub 2645 - cheese before bedtime cherub 3209 - anatidaephobia laser 176847 - kiss this [FORSALE] |
Posted By: Rupert
Date Posted: 21 Apr 10 at 7:16pm
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Boats which cannot plane are generally subject to the rule described, but boats which can plane will have a gradual transition between non planing and planing, which suggests that hard and fast rules on jib settings would be a mistake. Planing is one of those things which is difficult to define but blooming obvious when you do it! ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: ham4sand
Date Posted: 21 Apr 10 at 8:57pm
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i rem,ember more now... i think its when the boats stern overtakes the trough of the bow wave....according to frank bethwaite ------------- John Hamilton cherub 2645 - cheese before bedtime cherub 3209 - anatidaephobia laser 176847 - kiss this [FORSALE] |
Posted By: ellistine
Date Posted: 21 Apr 10 at 9:51pm
Had a look out for these to night and they definitely appear as the speed starts to build. I shall keep an eye on them  ------------- |
Posted By: Matt Jackson
Date Posted: 22 Apr 10 at 8:11am
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Isn't that what I said?
As it was from the Tasar manual I think our sources are the same as well.
------------- Laser 203001, Harrier (H+) 36 |
Posted By: ham4sand
Date Posted: 22 Apr 10 at 10:15am
yes but i was just saying it was the trough of the boW wave, not the crest, sorry matt  ------------- John Hamilton cherub 2645 - cheese before bedtime cherub 3209 - anatidaephobia laser 176847 - kiss this [FORSALE] |
Posted By: ColPrice2002
Date Posted: 22 Apr 10 at 2:45pm
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Yup, Really much more complicated, but some dinghies have an obvious transition - My old Firefly had a noticeable transition - usually needing a significant weight shift sternwards - between non-planing & "planing". My Solo has a trasition - but this is less severe (differnet hull shape) - however there are at least 2 different stages - I reached stage 2 in (non-forum) gusts of Force 6 - mega amounts of spray! On the other hand, the Merlin seems to lift (stage 1) almost imperceptibly. What Dinghy is the OP using?
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Posted By: JimC
Date Posted: 22 Apr 10 at 2:52pm
A 4 Tonner I believe, but the context is a tuning guide, so the creator of the tuning guide had a speed range in mind where certain settings need to be changed, so all she needs to know is when that point is reached. A discussion on what *is* planing would be better placed in the development forum... |
Posted By: ellistine
Date Posted: 22 Apr 10 at 3:20pm
Exactly. It related to jib sheet tension. When to keep it tight to aid pointing against when to let it off some to sail free. It was suggested that when planing there may be some advantage to sailing freer but a bit more reading suggests that there may not be much of an advantage doing this in a 4000. Still, at least now I know when we're (perceived to be) planing - other than when the daggerboard sings to us. ------------- |
Posted By: Guests
Date Posted: 22 Apr 10 at 3:37pm
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Frank Bethwaite either misunderstands or choses to mis-represent what planing is. It has nothing WHATSOEVER to do with sailing faster than "hull speed". There is no magic Froude number at which planing begins. As unhelpful as it is to real life, planing 'begins' when there is a stagnation point on the underside of the hull. |