Slip and performance numbers
 

I have a 1991 32' Fountain twin 502 with 530 hous bravo one 1.5 ratio I think.The props have been worked on but I dont know to what extent.It ran 74.9 mph on gps at 5200 rpm with 3 people on board and 1/2 tank fuel this weekend on the Hudson river.Can any one tell me my slip and if these number seem good.

Re: Slip and performance numbers
 

You really need to know or at least guess the pitch.

By my estimates here is where you are.

26P-12%
27P-16%
28P-19%
29P-21%
30P-24%

Re: Slip and performance numbers
 

23p on props,3 blade ,makes me wonder if ratio is different in drive.Its seems other boats like this are running higher pitch props then mine.

Re: Slip and performance numbers
 

I just ran it with 1:36 Gear and a 23P would be about 10% slip. Thats pretty good if that is the case.

We had a 32 Active Thunder with 1:36 and we spun 23P or 25P mirage three blades with a pair of Merc 502 465HP's and did about 77MPH. We went to 1:5 and spun 27P Mirage 3 blade and got 80-82MPH.

Are you trying to get more speed?

Re: Slip and performance numbers
 

I just purchased the boat and I'm trying to get ideas for performance upgrades over the winter.These are merc 502 mags with 415 horse.I would like to freshen them up and bump them up to 500 horse.But I want to make sure the complete package will still work together.I want to try and not over power drives or spend a fortune on prop set up.I would like more top speed and cruising speed.The hole shot now is strong and mid range is really strong,it pulls from 20 to 74 in no time.I like to take long trips and would like to cruise at 3500 rpm at a descent rate of speed.How can I tell drive ratio?and if they are 1.5 should I be running a bigger pitch?

Re: Slip and performance numbers
 

All good ideas and questions. I don't know exactly how you can tell the gear ratio without pulling them a part. From what you are telling me I would bet a lot of money they are 1:36 gears. The characteristic of 1.36 bravos are good hole shot and great mid range. If you want mid range, I would NOT change gears. Another reason I would think they are 1.36 is that if they were 1.50 you slip would be about 1%. That is impossible. If you went with 1.5 gears you could probably get 77-77.5 out of the boat but your cruise will suffer by about 5 mph given my experience.

As for props you need to talk to the experts. I have worked with Bblades for props. He is an ex-mercury racing prop guy. I also hear from others that throttle up knows there stuff too. They always say do your mods before thinking about props.

Re: Slip and performance numbers
 

It's important to know a few things about your boat before doing any prop work.

Accurate WOT RPM.
Accurate top speed.
Gear ratio.
Prop pitch.

If you are not sure about the gear ratio, don't trust what is on the gear case. The best things to do is put the drive in gear and turn the motor by hand and count how many engine revolutions are required for one prop revolution. 1 1/2 engine revolutions for 1 prop shaft revolution is a 1.5 gear ratio. 1 1/3 engine revolutions for 1 prop revolution is a 1.36 gear ratio.

The more accurate the testing numbers the better the prop work

If you are going to do engine mods over the winter wait to do your prop work until you have put your boat in the water and get some performance numbers. Then worry about the props.

No one wants to spend a fortune on props but remember, the only thing putting power to the water is the prop(s). If the props are not right then all the money spent on engine work is a waste of time and money.

Matt

Re: Slip and performance numbers
 

nordic95

here are some hard core #s, i have a 99 32 fever with twin 502 purchased the boat stock with 300 hrs.

75.6 gps 2 people 3/4 tank running 1.5 ratio bravo drives w 26 four blade hydromotives @5100 rpm

added livorsi prochargers and intercoolers, changed drives to 1.5 xr
tried bravo 30 4 bl not enough prop

using 32 4bl non lab running 89.7 mph @5100 rpm @approx 630hp per motor

but the best is cruise 3500 rpm 65 mph gps

currently adding cmi headers bring motors to approx 655 per to be done this weekend and will give those #'s as soon as i get in the water

i hope i see 93 mph but might have to spin 34 to get there.

Re: Slip and performance numbers
 

Do you have dyno runs on the motors?
If so, where is peak hp and torque?
Where is the rev limiter set?

Sounds like your modifications are working well. I would think the headers should be good for a few mph.

Matt

Re: Slip and performance numbers
 

Thanks guys for all the info,I'm putting boat in the water this Sunday to get some more starting numbers and I'm also going to try a set of Bravo one 24p four blades I borrowed from a friend.I just want to see how the four blade work compared to the 3 blades I have now.I will run gps number at different rpms with both sets of props.This way I can compare after motor mod this winter.Hey Matt did you do prop work for Epeek from Albany N.Y.?

Re: Slip and performance numbers
 

limiters set at 5250

no true dyno numbers

once i get hard rpm and speed numbers i will start labbing props and finish the dialing in

iam very happy so far.

Re: Slip and performance numbers
 

briana,
Your numbers parallel mine, I have a 96 27' Fountain with a ProCharged 502 mag @ 7lbs, upgraded full roller cam & heads etc for 700+ hp. Right now I am testing a 34 Bravo rh and getting some pretty good numbers,
3000 rpm 53 mph
3500 rpm 65 mph
4000 rpm 73 mph
4500 rpm 81 mph
5300 wot 89 mph.
I also ran a 31 Hydro Q4 and got 88.2 but I hit the rev limiter at 5450. I wonder what a 32p Q-4 would do?

Re: Slip and performance numbers
 

You may see 93 if you can turn the motors to 5250 after the headers.

Indy27,
Your slip is pretty high. How is the attitude of the boat? How does it get on plane. Are the 34 Bravo 1's stock? If you notice briana's speeds are the same as yours but he is running smaller pitch props at less rpm than you are.
Did you put a shorter lower unit on the boat? I would look at reducing the slip for some potential speed gains.

Matt

Re: Slip and performance numbers
 

Matt,
The boat gets on plane with no problem and carries the bow very well. I am running a stock 34 and standard lower unit. I know brianna is running smaller props but he also has twins vs my single!

Re: Slip and performance numbers
 

Ran the boat sunday with the new headers, kinda choppy and a lot of boats, live in sw florida its was nice out (no more hurricanes) so alot of people took advantage of the nice weather. couldn't get good # as i was with the wife and 5 yr old daughter, but i see a 3 mph gain at 3500 rpm but i have a question for brett and matt. how much bow lift can i see with prop work on 32 or 34, the bow seems to be glued more than before. the more hp it produces the more it rides flat.

no matter what i do with the drives 3-4-5 trim the bow does not want to come up (of course there is no tab involved)

this will become a problem at high speeds to wot as the boat will begin to chine

help me get some air under this thing.

brett, i will be sending the 30's this week.

Re: Slip and performance numbers
 

briana, Sounds good. We'll look for the 30's.

We can add some bow lift to the propeller.

It most likely will not cause chining but rather may cause the bow steering from the nose dropping. We should discuss this further.