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27-10-2014, 06:21 PM
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#1
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Registered User
Boat make: Sunseeker Apache 45
Cruising area: South coast and Channel Islands
Join Date: Jun 2014
Posts: 40
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Speed calculation
Hi All
Does anyone know how to calculate rough achievable speed with horsepower,revs,gear ratio,weight and water length?
ie
370hp 1.46 gear ratio 9 tonnes and approx 12m
Rob
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27-10-2014, 07:13 PM
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#2
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Registered User
Country: Belgium
Location: near Ghent
Occupation: engineer
Interests: boating, wakeboarding, snowboarding, fitness
Boat name: Outlaw
Boat make: Phantom 21ft
Engines: Yamaha 200hp
Cruising area: Zele / Kanaal Gent-Terneuzen
Join Date: Jun 2006
Location: near Ghent
Posts: 473
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for a speed calculation you need rpm ; ratio ; slip ; pitch
rpm ratio pitch slip
5000 1,46 15 20%
gives you 62km/h in every speed calculator
Is this a existing boat and motor ? If so, look up the WOT rpm and the proppitch. If not, start with a similar boat.
Hope this helps a little,
Kind regards, T.
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27-10-2014, 11:34 PM
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#3
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Registered User
Country: Ireland
Location: Dublin
Occupation: Boatbuilder
Boat make: Hydrostream V-king, 650SS OCR ,Ring 21, Ring 18, Phantom 18.
Engines: 300Hp Mercury 2.4, 130 Yamaha, Bridgeport EFI, XR6, Merc 200.
Cruising area: Malahide, Dublin
Join Date: May 2004
Location: Dublin
Posts: 1,803
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Google savitski formula ...
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27-10-2014, 11:44 PM
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#4
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Senior Member
Country: UK
Location: Devon
Occupation: Garage Proprietor
Interests: PowerBoat Racing
Boat name: If Only
Boat make: Bernico F3 OCR, Bernico Prototype Inboard, and some Ribs
Engines: Yamaha Pro V 115
Cruising area: UK, France
Join Date: Jan 2005
Location: Devon
Posts: 3,095
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Boat speed App on IPhone App Store !
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If Only
National Outboard Immersed Propeller Mono Record 103mph
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28-10-2014, 08:22 AM
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#5
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Registered User
Boat make: Sunseeker Apache 45
Cruising area: South coast and Channel Islands
Join Date: Jun 2014
Posts: 40
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I have looked at the iphone App. The thing Im not sure about is that you cant put in engine revs anywhere and they must play a part?
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28-10-2014, 09:42 AM
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#6
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Registered User
Country: Guernsey
Occupation: Postie
Interests: Heavy Heavy Metal
Boat name: Slayer II, Slayer, Pen15
Boat make: Phantom 19G-R, Bernico F2 Extreme, Ring 15
Engines: Evinrude 115HO, Yam 90
Cruising area: Channel Islands
Join Date: Aug 2009
Posts: 1,460
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There's two basic separate calculations that can be done.
One takes boat weight, horsepower, and a coefficient constant for what I assume is drag, which is always something of a guess based on some guidelines. This will give you a top speed estimate assuming you have it propped correctly and are turning the appropriate RPM
The second is a propeller slip % calculator. This involves speed, revs, gear ratio and propeller pitch.
In both cases there are lots of calculators online that allow you to calculate the missing value if you have the others. For instance if you know your current boat weight, speed and horsepower then you can fairly accurately work out your coefficient, which then means you can see what effects weight saving or increased power will have on your speed.
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29-10-2014, 06:06 PM
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#7
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Registered User
Location: West Coast of Norway
Occupation: naval architect
Interests: surface piercing props, stepped hulls, air entrapment hulls
Boat name: none
Boat make: PetterTintorera
Engines: Yamaha 90
Cruising area: West Coast of Norway
Join Date: Sep 2005
Location: West Coast of Norway
Posts: 888
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Quote:
Originally Posted by Ubatuba45
Hi All
Does anyone know how to calculate rough achievable speed with horsepower,revs,gear ratio,weight and water length?
ie
370hp 1.46 gear ratio 9 tonnes and approx 12m
Rob
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Sunseeker should be able to help with this?
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29-10-2014, 06:43 PM
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#8
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Senior Member
Country: UK
Location: Devon
Occupation: Garage Proprietor
Interests: PowerBoat Racing
Boat name: If Only
Boat make: Bernico F3 OCR, Bernico Prototype Inboard, and some Ribs
Engines: Yamaha Pro V 115
Cruising area: UK, France
Join Date: Jan 2005
Location: Devon
Posts: 3,095
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30mph !!
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If Only
National Outboard Immersed Propeller Mono Record 103mph
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29-10-2014, 06:52 PM
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#9
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Registered User
Join Date: Jul 2010
Posts: 52
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sounds like a Volvo D6? if it is and you message me all your specs you have i'll do a prop calc for you
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05-11-2014, 09:46 AM
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#10
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Registered User
Country: Catalunya
Location: Barcelona
Occupation: EMPRESARIO
Interests: sail, motonautica, scuba, MTB
Boat name: oshowatt
Boat make: PHANTOM 21
Engines: YAMAHA 200 V MAX
Cruising area: race boat
Join Date: Sep 2013
Location: Barcelona
Posts: 34
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A scopo didattico ricordiamo la formula per ricavare la massima velocità TEORICA di un'imbarcazione (in nodi):
Vt = (RPM / R) * P / 1215,2
dove:
Vt = velocità teorica
RPM = giri/minuto motore
R = rapporto di riduzione al piede
P = passo dell'elica in pollici
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facebook - olmarine powerboat team
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25-11-2014, 09:47 PM
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#11
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Registered User
Boat make: Sunseeker Apache 45
Cruising area: South coast and Channel Islands
Join Date: Jun 2014
Posts: 40
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D6-370
Looks like they will now be Volvo Penta D6-370 on DPR drives!
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25-11-2014, 11:30 PM
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#12
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Registered User
Country: solent
Location: solent
Occupation: still looking
Interests: wine, women, boats
Boat name: atlantic11, P9, no name.
Boat make: sunseeker, bonito,arrowbolt. ex. dry martini, scavenger
Engines: kad300, 7.4mercs, 5.7merc
Cruising area: south coast
Join Date: Aug 2014
Location: solent
Posts: 11
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Quote:
Originally Posted by Ubatuba45
Looks like they will now be Volvo Penta D6-370 on DPR drives!
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hi, is this for the apache? twin or triple? managed 48 mph on pdc with twin kad 300 (285hp) with clean hull, would think 55/60 given the extra 30% increase in power, less the increase in drag at the higher speed. how well will the D6s fit on the old engine beds? Hope it all goes well, keep us informed pete L.
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26-11-2014, 08:23 AM
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#13
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Registered User
Boat make: Sunseeker Apache 45
Cruising area: South coast and Channel Islands
Join Date: Jun 2014
Posts: 40
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Quote:
Originally Posted by peter law
hi, is this for the apache? twin or triple? managed 48 mph on pdc with twin kad 300 (285hp) with clean hull, would think 55/60 given the extra 30% increase in power, less the increase in drag at the higher speed. how well will the D6s fit on the old engine beds? Hope it all goes well, keep us informed pete L.
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Hi Peter
Yes this is for my Apache 45. She has twin KAD42 in her at the moment. i have owned her for about 12 years. The D6's are slightly wider than the KAD's so have a little work there to do but doesn't look too bad. I'm not sure what speed she will do, I'm thinking 42-45 knots depending on props and weather we try to squeeze a little more out of them.
Do you have an Apache?
Rob
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28-11-2014, 12:42 PM
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#14
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Registered User
Country: hamburg , germany
Occupation: electronics
Interests: boating, audio , PC
Boat make: Fletcher Arrowshaft 199
Engines: Yamaha 225
Cruising area: baltic sea
Join Date: Dec 2005
Posts: 115
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30-11-2014, 11:25 AM
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#15
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Registered User
Country: solent
Location: solent
Occupation: still looking
Interests: wine, women, boats
Boat name: atlantic11, P9, no name.
Boat make: sunseeker, bonito,arrowbolt. ex. dry martini, scavenger
Engines: kad300, 7.4mercs, 5.7merc
Cruising area: south coast
Join Date: Aug 2014
Location: solent
Posts: 11
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Quote:
Originally Posted by Ubatuba45
Hi Peter
Yes this is for my Apache 45. She has twin KAD42 in her at the moment. i have owned her for about 12 years. The D6's are slightly wider than the KAD's so have a little work there to do but doesn't look too bad. I'm not sure what speed she will do, I'm thinking 42-45 knots depending on props and weather we try to squeeze a little more out of them.
Do you have an Apache?
Rob
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hi rob, have tried to reply 3 times but they keep getting lost, will reply when can sort this out, all the best, pete L
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01-12-2014, 06:32 PM
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#16
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Registered User
Country: solent
Location: solent
Occupation: still looking
Interests: wine, women, boats
Boat name: atlantic11, P9, no name.
Boat make: sunseeker, bonito,arrowbolt. ex. dry martini, scavenger
Engines: kad300, 7.4mercs, 5.7merc
Cruising area: south coast
Join Date: Aug 2014
Location: solent
Posts: 11
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Quote:
Originally Posted by peter law
hi rob, have tried to reply 3 times but they keep getting lost, will reply when can sort this out, all the best, pete L
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hi rob, hope you get this mail. We replaced the 43s about 7/8 years ago with the 300s. use to get 34knts. through the water with the 43s. Volvo techs got 48 mph on the GPS on sea trials with the 300s. gps is variable with tide,wind etc. it is not possible to work out exactly the predicted speed from this as you need more hp per mph as the speed increases. it would seem likely that 50knts 58mph would be about right with the 370s Not sure i would like to drive the apache at that speed in a rough sea as they are a touring/sports boat, have had ours completely in airborne but dont think it would stand a lot of that treatment. Did you get a good deal on the d6. just a note on props, we were over propped on sea trials with C6s with on 1.5 drives, down 150 rpm which is not good for the motors, hope all goes well, pete L.
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