Great info, Stanley...thanks. I had *absolutely* no clue that I could
potentially increase the speed by using a higher pitch prop. My
impression was always that your prop should allow your engine to get to
it's max rpm in order to get max speed (which mine does)...guess I was
wrong. But still, I'm not sure I want to spend ~$200 for a new prop to
gain a few mph.

Stanley Barthfarkle wrote:
:Your theoretical top speed with your current configuration is 32.5 mph at
:5100 rpm.
:Your theoretical top speed with a 14 x 19 prop is 34.1 mph at 4800 rpm.
:Your theoretical top speed with a 14 x 21 prop is 35.8 mph at 4550 rpm.
:
:Prop info: (note- 15% is the average amount of prop "slip")
:http://powerboat.about.com/cs/propel...llingfacts.htm
:http://www.a1discountprop.com/propinfo.htm
:http://www.rbbi.com/folders/prop/propcalc.htm
:http://www.csgnetwork.com/marinepropcalc.html
:http://www.go-fast.com/Prop_Slip_Calculator.htm
:http://www.fishweb.com/recreation/bo...ps/props1.html
:
:
:
:"Bob" wrote in message
...
: It's a model 270D...2.15:1 gear ratio. When the boat was brand new
: (1972) and using the same pitch prop, the top-end was always 31-32 mph,
: so I feel good that I can get there with a rebuilt engine. Will a
: higher pitched prop, say a 14x19, drop the WOT rpms? If so, how does
: that equate to a higher WOT speed? Seems like it would do the opposite,
: but like I say I don't know much about props.
:
:
: Stanley Barthfarkle wrote:
: :Bob, what model is your outdrive? Do you know the gear ratio? Seems to me
: :that you should be able to swing a more aggressively pitched prop (more
: :top-end speed) with that engine, but it would help to know your outdrive
: :specs.
: :
: :
: :"Bob" wrote in message
: ...
: : I am using a standard (aluminum?) 14x17 prop, which seems to match the
: : boat well because my WOT is about 5200 rpm, but than again I don't know
: : much about props. I do have a Sting Ray hydrofoil but I prefer not to
: : use it unless I am going to be carrying a large load...it surely helps
: : me get up on plane faster, but it also reduces my top end by a few mph
: : as well as making the steering feel "tight" and not as responsive as
: : without it. One thing that is different on my boat than many of the
: : newer boats, is that the bow is closed so I can't put passengers up
: : there, which probably does not affect the top speed, but sure does
: : impact the ability to plane quickly when the boat has more than a few
: : adults in it.
: :
: :
: : Stanley Barthfarkle wrote:
: : : What prop are you using? Do you have a Sting Ray Hydrofoil? If not,
:get
: : ne. Boat planes better, and it allows use of a higher pitched prop
14 X
: :21
: : :SS cupped in my case). Less cavitation, and no "rooster tail"- energy
: :that
: : :would have been wasted with a rooster tail is sent rearward,
:increasing
: : ropulsion.
: : :
: : :
: : :"Bob" wrote in message
: : ...
: : : Dang, how do you get so much speed out of your little Volvo engine?
:I
: : : have a newly rebuilt AQ130C ( 4 cyl. 130 hp) and it only takes my
:boat
: : : up to 31 mph at WOT, about 5000 rpm with two adults in it. My boat
:is
: : : a 17' fiberglass v-hull and weighs about 2000 lbs I would guess, and
: : : has a Volvo 270 outdrive on it.
: : :
: : : BTW, it consumes just 3-4 gph at cruise speed (4200 rpm, 27 mph).
: : :
: : : Bob
: : :
: : : Stanley Barthfarkle wrote:
: : : :1985 Bayliner 1952 cuddy
: : : :18.5' fiberglass 'modified V' hull
: : : :19.5' Length over all
: : : :2200 lbs dry weight
: : : :1985 Volvo Penta AQ125B 4 cyl 105 hp 4 stroke
: : : :1 barrel Solex carb 35 mm
: : : :Volvo Penta 270 Stern drive
: : : :14 X 19 modified SS 3-blade prop (14 X 21 effective)
: : : :StingRay Hydrofoil
: : : :35 mph WOT @ 4800 RPM
: : : :32 mph cruise @ 4400 RPM
: : : :
: : : :Premium unleaded fuel (92 octane)
: : : :4 adults & 1 dog, ski equipment, coolers, etc-
: : : :6-7 gph WOT
: : : :5 gph cruise
: : : :
: : : :
: : : :
: : : :"Matt Lang" wrote in message
: : : . com...
: : : : Guys,
: : : :
: : : : I am thinking about getting a harbercraft jetboat ... these
:things
: :are
: : : : made from aluminum and have the 175 HP Mercury sportjet..
: : : :
: : : : So far so good ... Now what raises the fuel warning flag are the
: : : : terms:
: : : :
: : : : - jet
: : : : - 2 stroke
: : : : - carburator (two of them
: : : :
: : : : The boat will burn about 5 gallons per hour at 30 mph... now I
:was
: : : : wondering how this compares to a similar sized fiberglass hboat
:with
: : : : 115-150 HP 4 Stroke outboard..
: : : :
: : : : What is the fuel you burn at cruise speed and WOT, whats your
:boat
: : : : size/weight and what motor are you running ..
: : : :
: : : : I am interested in how the relatively light alu jetboat compares
:to
: :a
: : : : more conventional boat with 4 stroke motor..
: : : :
: : : : Any info is appreciated
: : : :
: : : :
: : : : Matt
: : : :
: : : :
: : :
: : :
: : :
: : :
: :
: :
: :
: :
:
:
:
: