More speed?

billy no boat · 04-10-2010, 09:07 PM

Evening.

we have a Cougar R9 *cough rib cough* and looking for a little more speed.

currently it has a steyr 256 (mo256h45) through Bravo 1 drive spinning a 25 inch high 5 stainless prop.

At the moment we are seeing max 4200 rpm at 45 kts on the gps. dont get me wrong, most of the time this is enough but would like to know if theres anything more to be had.

We usually run with pretty full fuel load (260L) and 2 up so...... any suggestions on improving the speed a little?

The boat and engine is 5 years old with total hours to date of 145...

Props are clearly a dark art so appreciate any suggestions....

bor · 06-11-2010, 10:37 PM

Quote:

Originally Posted by billy no boat

Evening.

we have a Cougar R9 *cough rib cough* and looking for a little more speed.

currently it has a steyr 256 (mo256h45) through Bravo 1 drive spinning a 25 inch high 5 stainless prop.

At the moment we are seeing max 4200 rpm at 45 kts on the gps. dont get me wrong, most of the time this is enough but would like to know if theres anything more to be had.

We usually run with pretty full fuel load (260L) and 2 up so...... any suggestions on improving the speed a little?

The boat and engine is 5 years old with total hours to date of 145...

Props are clearly a dark art so appreciate any suggestions....

Hi there ,it looks like your a bit overproped your engine can make 4500 rpm max so you have to go to a smaller pitch to get to 4500 rpm WOT .

Also you can calculate your prop slip number to see if it's not to much slip.
what gear ratio is your drive ?

I have a 32 hustler whit 2 diesels and xr drives and had first had 32 maximus props on it wich are great but just to much came no further then 3600 rpm and 68mph on gps and need 3800 ,now I have 34 bravo's and run 3750 rpm and do 72mph on gps

cheers,

bor

larby · 07-11-2010, 09:40 AM

I'd imagine they'd be much closer to 4500rpm with less fuel on board. How much other kit do you carry, and where is it positioned? It's amazing what a difference all those little things can make. Shifting things from front to back can affect the balance of the boat and really change matters.

Another thing to consider before changing about for ultimate top speed is drivability. You could probably see a gain in speed from less blades on the prop, higher pitch etc, but it'd likely be a pig to get on the plane with several people on board and it wouldn't accelerate.

There's a cougar R8 over here which isn't propped to go as fast as it could, but it accelerates like a sportscar with no noticable aeration and is generally the best set up, most useable boat I've ever had the pleasure of driving. I wouldn't change a thing on it, even if it could do 20mph more.

James

billy no boat · 07-11-2010, 11:56 AM

thanks for your replies.

we dont carry much on board (as theres not much dry storage) anchor up in the bow locker. usual safety stuff under the seats and if we have any kit for the day it goes up under the table in the bow.

fuel load is difficult to tell to be honest. i am told the tank is 270 L but looking at the original spec from when the boat was built it says 200L. the fuel gauge is very inaccurate as it it shows empty and i can only get 110 L in at fill up so at the lightest its 90 L fuel and at heaviest 160L. even with the lightest fuel load we have seen, max revs were 4100.

maybe some prop testing in the new year is worth a try!

agree with what you say about all round drveability. theres no point having a quick boat that needs to be towed over the hump!

boat is coming out of the water for a few weeks this month and Steyr have suggested they can increase the boost pressure (as the engine is now out of warranty) to give us a little more although im not sure this is smart as i dont want to jeopardise the engine for the sake of a few kts!

i havent had the chance to drive Tony's boat yet but it looks lovely! he does have the luxury of additional 100 horses on us!

larby · 07-11-2010, 05:28 PM

With what you've now said about fuel load and revs, it probably is worth doing a bit of prop testing. I'd go down in pitch a couple of inches on the same style of prop at first to give a fair comparison, then try other types of prop. A 4 blader may work well, not sure I'd go as low as 3, I've heard the handling gets interesting on the cougars with only 3 blades.

All that said, there's others on here who know far more than me about this (and everything else!), hopefully one of them may chip in too?

Cheers, James

billy no boat · 07-11-2010, 09:03 PM

thanks James,

the current prop is coming off and going away to be repaired first (few dings from the previous owner)

then we try some new ones but its a pain with the outdrive as the boat has to come out to change the prop!!

got some work to do before christmas with the electrics and re rigging the console. then see what we can do. interesting what you say about 3 blade on that hull! theres some mixed views on it but so far, i have been well impressed in a range of conditions. (leisure only!)

larby · 07-11-2010, 09:55 PM

Assuming you're sending the prop off to someone decent like propeller revolutions, why not get them to take an inch or 2 of pitch off while you're at it? May as well play around with the prop you've got to save you having to buy others, especially if it needs repairing.

It's amazing what a place like that can do to help. Give them a little information on how the boat runs now and what you want from it and they'll work magic with it for you. Pitch, diameter, cupping, blade area, rake etc etc can all make a huge difference and nobody knows what to change for what results better than the experts. I've been stunned by the results of every bit of prop work they've done for me.

James

billy no boat · 11-11-2010, 07:43 PM

Im sure it's me being thick but can't make my head understand props!

On the basis we are pulling 4200 rpm and max is 4500 if we drop 1 inch on the pitch that should give us an extra 200 rpm ish.

Currently we cruise at 3600 rpm doing around 33 kts. With the new lower pitch prop are we likely to get same speed at revs or faster at same revs?

Can see how it might increase top end as it's allowing the prop to spin faster but will it make any difference anywhere else in the rev range?

Sorry for the dumbass question!!

larby · 11-11-2010, 08:06 PM

You may see same speed with more revs at that kinda point, but anything can happen really.

The idea of using less pitch to gain revs and hopefully pick up speed is that you want your engine in it's optimum power band at full speed.
ie, your motor is most powerful at 4500 rpm, so you want it there at full speed.

Hope that makes sense,

Cheers, James