Afishionado Posted April 18, 2007 Report Share Posted April 18, 2007 Paul (D) on another thread says .... My 520 planes at around 5 to 6 knots with the smart tabs fitted and that is with a fair amount of weight in the back as well. This seems to defy the laws of physics and hydrodynamics? An object moving through/across the water needs several factors to coincide before sufficient lift is created to remove the influence of water drag on the hull and allow the whole to rise untill the total weight is riding ON the water film rather than through it. For the life of me I can not see this happening to any solid hull boat at 5 or 6 kts. So either Pauls estimation of his speed is well off or the GPS is wrong or the boat is not planing but just getting up ready to lift on to true planing speed. The formula for planing speed is very similar to that of an aircrafts needs to fly. To overcome (drag), gravity (weight), airflow in the terms of velocity (lift) and I can not see the figures adding up to a planing speed of 5knts Mad Mike Quote Link to comment Share on other sites More sharing options...
jack Posted April 18, 2007 Report Share Posted April 18, 2007 You tell 'em Mike. What an uncanny knack you have of stirring up the...I mean creating a controversy,Although my Zodiac appears to"plane" at a very low speed,but I dont have any way of telling speed whilst useing it..Keep up the good work..jack Quote Link to comment Share on other sites More sharing options...
Adam F Posted April 18, 2007 Report Share Posted April 18, 2007 I find it easier to tell when you have 'fallen 0ff' the plane as opposed to startef to plane. BW started to plane about 12/13 knots, OotB startes about 13/4 - below this it is a fine line between heavy semi displacement and planing. The smart tabs I fitted knocked about 1 knot of the min plaing speed. 5 knots is very slow, I would be surpised if even jacks little Zodiac plans at 5... Quote Link to comment Share on other sites More sharing options...
TomBettle Posted April 18, 2007 Report Share Posted April 18, 2007 With you guys on this, although I am not sure why we are having the conversation..... I had a little Quicksilver 430HD inflatable. As far as boats go it weighed nothing. It had a planing hull created by an inflatable keel. It did plane remarkably slowly, but even this was about 8 knots, much faster than 5 or 6.... Quote Link to comment Share on other sites More sharing options...
plaicemat Posted April 18, 2007 Report Share Posted April 18, 2007 Thank God for all this; I was about to chop my Warrior in for a bl@@dy Orkney. Terry. Quote Link to comment Share on other sites More sharing options...
Newboy Posted April 18, 2007 Report Share Posted April 18, 2007 News Flash orkney invents super planning hull which plans at 5 knots ...... Quote Link to comment Share on other sites More sharing options...
Paul D Posted April 18, 2007 Report Share Posted April 18, 2007 My estimate was a little on the slow side !! - Realised this going out of Christchurch harbour the other day Probably more like 10 knots. Quote Link to comment Share on other sites More sharing options...
jack Posted April 18, 2007 Report Share Posted April 18, 2007 Relax Paul.The beggars are "winding you up " led by the chief "winder" who shall remain nameless. jack... Just to add to this,I can turn head into a strong tide ,and plane without moving an inch over the ground.so its all relative. Quote Link to comment Share on other sites More sharing options...
charlieannear Posted April 18, 2007 Report Share Posted April 18, 2007 Hooray, my Shetland doesn't plane like a proverbial brick after all! Quote Link to comment Share on other sites More sharing options...
Afishionado Posted April 18, 2007 Author Report Share Posted April 18, 2007 Relax Paul.The beggars are "winding you up " led by the chief "winder" who shall remain nameless. jack... Just to add to this,I can turn head into a strong tide ,and plane without moving an inch over the ground.so its all relative. Possibly an excess of flatulence on your part Jack. Sorta like a built in 'ground affect' We have just bought a little inflatable with a 4hp engine and that gets flying like a saucer when there is only one light person aboard. Me? It goes down half an inch deeper and needs a minute or two to decide to move Mad Mike Quote Link to comment Share on other sites More sharing options...
jack Posted April 18, 2007 Report Share Posted April 18, 2007 Quite right Mike,I forgot to mention being in a boat at the time !!,My 12' Zodiac has a 10hp engine,So there !! Unfortunately I dare'nt open it up as ,even with an extension tiller,it's downright scary .Very little control at all.I have the larger engine for tide punching when "2 up" with 2 dogs ;anchors ropes fishing gear etc.in my Welsh estuary.. I am too old and cautious to belt the hell out of it [perhaps 30 yrs ago I would have.] Quote Link to comment Share on other sites More sharing options...
Afishionado Posted April 18, 2007 Author Report Share Posted April 18, 2007 Welsh estuary ?? Which one Jack? Mad Mike Quote Link to comment Share on other sites More sharing options...
jack Posted April 19, 2007 Report Share Posted April 19, 2007 The Mawdauch. [exits at Barmouth.]..jack. Quote Link to comment Share on other sites More sharing options...
duncan Posted April 19, 2007 Report Share Posted April 19, 2007 hmmmm - so a 9.8hp on my tender (3m) is a little excessive eh Jack? to me displacement is displacement - anything else is technically planning although some hull forms are not designed to give the necessary lift to plane cleanly and are clasified as semi displacement (semi planning!) - on the other hand they don't have large resistance humps either so work well at medium speeds. shorter the waterline length of a boat (or object) and the lower the speed it must be planning or it sinks as a result of it's sternwave. simple fysics. 520 will, based on a mwaterline length of 4.8m, have to be planing at 5.57 knots or sink - well the recently modified figs actually suggest that it could survive up to 6.13 knots but ........... Phaeton can get to about 8.5 knots before it hits R1 and needs a huge injection of power to go faster (and over the hump).. Fortunately the turbo comes in at 8.2 knots.....and delivers that power! I am fully planning at 10 knots but don't get the full hydrodynamic effect from the hull untill 14knots normally laden - at which point I am properly (fully) trimed out at the drive as well. Quote Link to comment Share on other sites More sharing options...
Afishionado Posted April 19, 2007 Author Report Share Posted April 19, 2007 520 will, based on a mwaterline length of 4.8m, have to be planing at 5.57 knots or sink - well the recently modified figs actually suggest that it could survive up to 6.13 knots but ........... ????? SINK??? What disapear under the waves?? All that happens is either there is sufficient power to overcome the uphill gradient of the 'hump' and the boat progresses to plane or if there is more power but not sufficent to plane then the bow angles higher and the stern sinks lower into the simplistically speaking, hole in the water that the engine (prop thrust) has dug. Mad Mike Quote Link to comment Share on other sites More sharing options...
Mike Fox Posted April 19, 2007 Report Share Posted April 19, 2007 I love this thread. Being constrained to around 6 knots with my 6 tons and 28 h.p. I have nothing but admiration for anyone who can contemplate planing! Still...I do get good miles per galleon.... Mike Quote Link to comment Share on other sites More sharing options...
jack Posted April 20, 2007 Report Share Posted April 20, 2007 Mike,What you need is an area of sea with a long downhill slope.I have photo's in my collection of several areas like this but unfortunately I cant remember exactly where they are... jack Quote Link to comment Share on other sites More sharing options...
Mike Fox Posted April 20, 2007 Report Share Posted April 20, 2007 I have managed over 10 knots on said slopes Jack...but it's a bit of a white knuckle ride, and totally unsuitable for fishing when it's like that! There was one time the prop was freewheeling so fast, that I reckoned I might have been able to bump start it....but must admit was too nervous to leave the helm to try to lift the decompression levers to try it. Mike Quote Link to comment Share on other sites More sharing options...
duncan Posted April 20, 2007 Report Share Posted April 20, 2007 Jack - when I've been in those I haev never felt the opportunity to photo them - like MikeF I am hanging on to the tiller! Afish....you have answered your own point - what happens when the stern sinks so low in the hole......... it's been the documented cause of lose to a number of craft over the years; tugs being the most suseptable class of craft! Quote Link to comment Share on other sites More sharing options...
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