Cant get this Starcraft right.....another prop

[msojjo]

So i get my new prop on the boat and took it out this past weekend with four people (750lbs) a half tank of fuel (25 gal). The prop is a 21 pitch three blade stainless steel mirage plus and it seemed to perform ok out of the hole. My first question is on the performance vent system. Do i just pull one plug out at a time untill i'm happy with the performance, or all at once because you have to pull the prop and pop the plugs from the inside of the prop, will it even work because i have the corsa thru hull exhaust. So the real concern to me is the wot rpm's......Like i said i'm running a 20 foot deep v bowrider with a 350mag with 300 hp and a bravo 1 drive with 1.50 ratio. The boat is 3300lbs dry so people and fuel just over 4000lbs. I was running at 4200 rpm and 58 mph, checked aginst gps and speedo is 3 mph fast across the board, it was reading 60- 61. It's a brand new tach so i wouldn't think that its off, but who knows. So do i drop down in pitch again? My wife is going to kill me......

 

[Raystownboater]

Re: Cant get this Starcraft right.....another prop

When trying props at the marina, the tech told me that 4200rpm at wot is right where you want to be.

 

[msojjo]

Re: Cant get this Starcraft right.....another prop

When trying props at the marina, the tech told me that 4200rpm at wot is right where you want to be.

Normal operating range for my motor is between 4600 and 5000 rpm, so i'm 400 rpm too low yet......is this ok, or am i lagging the motor.

 

[msojjo]

Re: Cant get this Starcraft right.....another prop

duplicate

 

[Robbabob]

Re: Cant get this Starcraft right.....another prop

You are lugging the motor if the tach is set/reading correctly. I didn't want to respond earlier as I do not have input for the type of prop you are using.

Odd thing is... you are reaching great speed at the stated rpm.

Let's review weight of 3300 dry + 750 in people is 4050, then add 25 gal gas at 8+ per gallon is 200+ pounds, plus oils, ice chests and other "gear", you may be looking at 4500 easy. Just sayin'

Need to confirm the tach is reading correct, , , then someone with knowledge of this prop will chime in on the adjustments of removing plugs.

Keep it coming!

 

[msojjo]

Re: Cant get this Starcraft right.....another prop

Your right, when i lighten the load the rpm's and speed will go up, and then i should be at the bottom end of my suggested range. I'm going to check the tac, but i'm positive it's on, and set correctly.

The prop is the 21 pitch mirage plus with the performance vent system, and was told that these work very well with the bravo drives. I'm hoping that pulling some or all of the plugs will help with hole shot at least a little. My top speed is unbeliavable, is that due to having the bravo drive instead of an alpha with the differend gear ratios?

 

[Robbabob]

Re: Cant get this Starcraft right.....another prop

Actually, you want to be within the rpm spec at all times, thus the "window" they give. Typically, your loaded condition will be within range at the lower end so empty will be at the higher end; or something to this rate.

Read a little on the PVS http://www.mercurymarine.com/media/mercury/pdfs/service-and-support/props/PVS.pdf

Read the details.. Since you have the prop, do the testing and find out what happens with certain holes open. It looks like there are several between each blade. I would always stay consistent between the blades, allowing uniform exhaust flow to each one.

Good luck.

 

[Tail_Gunner]

Re: Cant get this Starcraft right.....another prop

I thought a 21 would be a bit steep...Ok your numbers were they taken with or without people it is very important. Your over propped if those numbers were given without peole in the boat...And pvs wount help

 

[msojjo]

Re: Cant get this Starcraft right.....another prop

Tail gunner,
Thoes numbers are with people in the boat.....4 adults about 750 in people, 25 gal of fuel another 200 two batteries, two sets of skis, two ancors, rope ect, propably an extra 300. Empty weight of the boat is 3300, plus people and gear 1250lbs give or take a little, so total is 4500 or so.

 

[msojjo]

Re: Cant get this Starcraft right.....another prop

And pvs wount help

Is that because of the bravo drive with all of the exhaust relief ports, or switchable exhaust, both......

 

[Tail_Gunner]

Re: Cant get this Starcraft right.....another prop

Im sorry to do this but your tach is still off.... with your combo... 4200rpm.. 21p...1.50 nets 56 mph with 0 slip. Be patient and find a tach that will verify your boat tach on the fly. A word about boat tachs....there pretty...there marine proof (rugged) but not accurate at all (for the most part). On the brighter side i think your propped dead on 60 mph loaded boat 20' is carzy fast...without a load...that probably pushing 65-67 mph...In addition thats a heavy deep v and loaded like it is should be a struggle out of the hole and you have no complaints

PVS just allows the prop to spin up or slip on launch....air bubbles escape infront of the blade casuing slip and the prop starts to rev much higher...Now at a certain point the water stream closes those holes and the prop hooks up to its full potential..that occurs arond 20 to 30 mph..Your out of the hole now and no longer need revs its spinning quite nicely

A bit like reving up a car to say 3000...dropping the clutch and the tires break loose spinning hard...at some point they hook up and you get full traction...In the case of PVS the outise water pressure on the prop barrel closes the holes and you get hooked up .

 

[msojjo]

Re: Cant get this Starcraft right.....another prop

I'll have to verify the tach then i guess, i won't be up to check for the next couple of weeks, that should give me the chance to find something.....The other thing i need to check is if the pvs works or not for my application, i popped all of the plugs out but haven't tried it, who wouldn't like a little better hole shot, if i just could get that motor to rev up to 3500 out of the hole i think that would be absolutly perfect.....great hole shot and an awsome top speed. So, do you think my rpms are closer to the 5000 mark?

 

[hidef]

Re: Cant get this Starcraft right.....another prop

Based on 11% slippage if I did the math right your tach should be reading 4860. I would say you are propped correctly since you are 58 mph.

 

[msojjo]

Re: Cant get this Starcraft right.....another prop

So i was able to get up and get the boat on the water again and do a few more tests on it. I put it back on the water on saturday morning and me and the wife jumped in and did a little wot testing on the lake. I'm 200lbs and her 130lbs, and just over a half tank of fuel, guessing 35 gal. First of all i took the pvs plugs out of the prop before i put the boat in the water, and it does make a difference. My rpms were jumping up to 3500 coming out of the hole and with a light load pulls the boat out very quickly with half throttle. So the wot numbers this time with a lighter load was 63mph and rpms were at 4550 and i ran out of lake fast, so there may have been a little more in her. So for cruising this prop is pretty damn good. Even when the boat is heavly loaded it dosn't do so bad. I had 1350lbs of people on the boat at one point, adults in the back and kids in the front, so i had 7 adults and 8 kids, it did take a while to get up and going, but i did get on plane and it handled great. I also am able to pull slalom skier up with 3 adults in the back of the boat and tubers and skiers with a fuller load. It's so nice to post good news on here for once.

 

[Tail_Gunner]

Re: Cant get this Starcraft right.....another prop

So i was able to get up and get the boat on the water again and do a few more tests on it. I put it back on the water on saturday morning and me and the wife jumped in and did a little wot testing on the lake. I'm 200lbs and her 130lbs, and just over a half tank of fuel, guessing 35 gal. First of all i took the pvs plugs out of the prop before i put the boat in the water, and it does make a difference. My rpms were jumping up to 3500 coming out of the hole and with a light load pulls the boat out very quickly with half throttle. So the wot numbers this time with a lighter load was 63mph and rpms were at 4550 and i ran out of lake fast, so there may have been a little more in her. So for cruising this prop is pretty damn good. Even when the boat is heavly loaded it dosn't do so bad. I had 1350lbs of people on the boat at one point, adults in the back and kids in the front, so i had 7 adults and 8 kids, it did take a while to get up and going, but i did get on plane and it handled great. I also am able to pull slalom skier up with 3 adults in the back of the boat and tubers and skiers with a fuller load. It's so nice to post good news on here for once.

Good to hear..IF you get the chance a stilletto Bay Pro 11 in a 20 pitch 4 blade ss would be a absloute winner for that boat. Tons of midrange very smooth feel....It to has the pvs and when it hooks up in that ride it would feel like a old 4 barrel carb kicking in on a big block..I doubt there would be a speed loss and it should pickup a few hundred rpm...Have fun with that sled..


They can be had for 300 if you look