how fast

[lobbers]

can anyone shed some light on what sort of speed i may get out of my yam 200 prov with 21" prop please:)

[Burty]

If the sequel is a light boat a 21" may be alittle on the small side but i recon you should see at least around the 60mph

[Cookee]

It depends on the gear ratio of the gearbox as well.

[Gav]

Originally posted by lobbers
can anyone shed some light on what sort of speed i may get out of my yam 200 prov with 21" prop please:)


Not fast enough cockwipe!!:bang: :drain: :lol:lol:

[lobbers]

so what would be a better size prop to use:hugegrin:

[Gav]

Originally posted by lobbers
so what would be a better size prop to use:hugegrin:

two bladed Seagull prop..........worked a little:bang:

[lobbers]

and stiil you would be following:drain: :drain: :drain:

[Burty]

Originally posted by lobbers
so what would be a better size prop to use:hugegrin:

Whats your gear ratio?
what rpm is peak power on your engine?
how high you running? i.e where is your prop shaft in relation to the bottom of your transom?

[lobbers]

not sure of any of that just brought engine cos looked good and prop is about 4ft away as not fitted it yet wanted to get as much info as poss before so to get it right when fitting it

[Burty]

if it the same sort of spec as a 200 merc with 1.87:1 gears and you are looking for top speed thus sacrificeing a little on pull out by mounting the engine high you may see the magic 70mph but you may find you need around a 23" prop to keep the revs down but best thing to do is find out where peak power is then run it with what you got and see what revs you get flat out then prop up or down accordingly.

[lobbers]

ok thank i,ll have to see how she goes know where there is a 4 bladed phirana 24" prop:hugegrin:

[Gav]

Originally posted by lobbers
ok thank i,ll have to see how she goes know where there is a 4 bladed phirana 24" prop:hugegrin:

Feck off!:flame: :hot: :wank:

[lobbers]

now thats not being very sporting is it:frog: :jaw:

[Jon Fuller]

I think the Yam's are lower revving than Merc's, topping at summat like 5500

[Steve]

Running a Yam Pro V 200 on the back of a Ring 21E with a Yam 23" prop & getting just under 70mph @ 5800 rpm.

Have tried a couple of 4 bladers & gain on pull out but loose a couple of mph at the top end.

Not sure how the weights of the boat compare though.

[Cookee]

If you put all the data into this - speed calculator (http://www.rbbi.com/folders/prop/propcalc.htm) you will be able to work it all out!

[Thunderbird Racing]

i was running my yam 130 at 6400 no problem this year after cutting the rev limiting cable.

[FrenchPhil]

Isnt there a speed calc out there with boat weight ? It definitly has an impact on speed.

[Cookee]

No because there are other factors involved such as hull design. The prop calculator will give you a maximum possible speed or if you know that the amount of slip but that's all.

[BluFin]

Originally posted by FrenchPhil
Isnt there a speed calc out there with boat weight ? It definitly has an impact on speed.

Correction is made under the slip of the prop,
identical set ups but with differing weights will have differing slip percentages.

There are a lot of questions on props must post my excel spredsheet. er Damm!! must make it a zip first !!

[Jon Fuller]

Originally posted by FrenchPhil
Isnt there a speed calc out there with boat weight ? It definitly has an impact on speed.

There's a formula for comparing boats of a similar design, with differing weight and Power, that I know as the 'Levi' formula. but it basically says, to double your speed, you must quadruple your power.

[BluFin]

Originally posted by Jonny
......., to double your speed, you must quadruple your power.
How strange that works almost exactly for take home salary for ex wives to double your income you must quad your salary:hugegrin:

[Jon Fuller]

Ouch!

[BluFin]

Attached zip of Speed calc on Excel S/Sheet
Type known info in yellow boxes, you must know your gear ratio

Slip can vary greatly

[dbe1]

I ski raced a Yam Prov 200 set on a power lift on a Phantom 21, hit 75mph ,6800 revs. ran a 23 Prov stainless prop race prepared by Pole Propulsion, rev limiters removed, blue printed, 250 yam heads, Boysen reeds, terrific acceleration out of the hole, never missed a beat in over 4 years of hard racing.

[Matt]

Also the knowledge base on www.go-fast.com is pretty good for calculations & predictions.

[FrenchPhil]

http://www.go-fast.com/boat_speed_predictions.htm

Is what I had in mind weight wise.

[Jon Fuller]

Phil, gotta be a fluke, but that calculator said of my boat, based on 6600lbs, 650hp and 225 'constant = 71mph, which is precisely what it does.

There has to be hint of luck in there tho', coz you could have the exact same input figures, with another hull design, weight distro etc, and get a very different outcome.

[FrenchPhil]

Well John, I tried a few scenarios & it's pretty close. Anybody try with 16-20' Phantoms
with 90-280 hp ?

[BluFin]

Dont rely on it for multihulls I have just run the thing from my old raceboat data from 84 it calculated out at 116 MPH
(I my what would have been very wet dreams)
Never not even close.

It does state cats are a variable though

What does the specter weigh TD have you run it through that link?

[Jon Fuller]

yeah, but did you put your all up weight in as 'pounds'?

[jw.]

Originally posted by Jonny
Phil, gotta be a fluke, but that calculator said of my boat, based on 6600lbs, 650hp and 225 'constant = 71mph, which is precisely what it does.

There has to be hint of luck in there tho', coz you could have the exact same input figures, with another hull design, weight distro etc, and get a very different outcome.

It must be that constant at 225 is dead right for your boat at the weight you put in.

[Jon Fuller]

Actually, when I read the instructions properly, and put in the correct HP (after transmission losses) and the exact weight, rather than approx, the numbers changed, now it seems my boat has a constant of 235

[BluFin]

Yep in pounds, could be in the transmission loss, being great than anybody realised .
great to play with eh !!