Prop and speed is making me question my ratio..

[BajabossJD]

Hey guys!

I currently have a 496 stroker with minimal mods. It has gobs of torque, but maybe just under 400hp.

I installed the engine and got it broken in. I turned at Mirage 23+ 5000 rpm and hit around 60.

I wanted to lower my RPMs so I bought a Mirage 25. It ran 61 at 4750 rpm (good hole shot).
.At the time I had 60 gallons of fuel in the tank and also had a BUNCH of water in the hull (had new engine stringers installed..the fiberglass guy left a tiny plug in the drain pipe underneath the deck..where it empties into bilge)..Long story short..I had a very heavy boat for a while and didn't even know it (2 months of rain!). I drained it out and I bet 300-400lbs of water came out.

(I also removed 100+ lbs of weight from the bow area (removed marine AC unit from from Bulkhead)

I instantly could feel how much lighter the boat is now. The hole shot is CRAZY STRONG and my WOT speed is 59-60 at 4850-4900 when trimmed correctly. I can plane right away with no Tabs.

Why did I lose speed by taking out 400l-500bs out of the boat?? I notice the standard Mirage blows out when trimming up MORE compared to the Mirage plus. Am I not getting the bow lift I need to build more speed?

I am at 48-49 MPH at 4000rpm.

I am at 42 at 3300.

I am not expecting a crazy fast boat after this engine build.. but with these numbers..I am starting to think I have a 1:65:1 Bravo 1. My slip numbers are very high using the 1:5:1 ratio. Would the 25p Mirage Plus be my next step for more lift? (more cup).

Thanks!
Joe

 

[alldodge]

Sounds like you have the same issue going on as I do. Rebuilt my hull and pulled 3 to 400 lbs out of the boat on the stern due to water soaking in on my Formula 27PC. Rebuilt my 502 from 425hp to 530hp and my WOT is the same plus maybe 1 mph, hole shot is much better. The boat is now real touchy with trim and my slip numbers are 20 to 25 percent.

We could work together on this one, but my thought is, the extra hull weight kept the prop in the water deeper. Being deeper allowed for better bite. When we take off the boat is lighter and comes up a lot quicker. Coming up quicker is also a determent when we need more bite at top end.

There is also a possibility the hull has reached is max hull speed

My plan for next year is to bring some sand bags or some more folks along to sit in the rear to see what happens

 

[Tail_Gunner]

Read This First!! [COLOR=#6A6A6A !important]December 22nd, 2008, 10:11 AM[/COLOR]



ESSENTIAL DATA REQUIRED
When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

The below link would be a much more thorough list of data to provide if you're looking for detailed performance numbers,
http://forums.iboats.com/prop-questi...ml#post2336620


Just a few more lines to fill....what type of boat and how heavy

 

[alldodge]

Only thing missing is 2 and 3, number 6 is there other then year and the boss 232 weight is out there
http://media.channelblade.com/boat_graphics/electronic_brochure/company5069/29615_f.pdf

 

[Tail_Gunner]

Only thing missing is 2 and 3, number 6 is there other then year and the boss 232 weight is out there
http://media.channelblade.com/boat_g...69/29615_f.pdf

Joe
Baja Boss 232
7.4 Carb W/ Bravo

I See says the blind man.

Length 23'4"– 7.11 m Beam 8'4"– 2.54 m Weight 3,900 lb – 1,769.0 kg Draft 34"– 86.36 cm Deadrise at Transom 23? Fuel Capacity 74 gal – 280.0 L Passenger Capacity 6 Sleeping Capacity 2

60 mph 454 4000lbs not to bad. Ratio wont change thing's your fighting wetted hull surface i had this problem once and went to a high rake large 4 blade prop for bow lift....Id pop off the brand but its a bass boat prop but i got the lift i was looking for and a 8% slip ratio.

 

[BajabossJD]

Thanks for the input guys. I know its not the fastest hull around for the size..but losing the weight and slowing the boat down tells me I have the wrong prop. My slip numbers are over 20%.

I had a 21 mirage plus on my old engine (330hp) and it ran 53mph at 5400rpm.

My 23 mirage plus on my old engine (330hp) was 56-57 at 4600 rpm

I was able to push that 23 mirage plus to 5000 and 61 with my new engine (390hp)

I seem to be able to push the 25 mirage with no issues..I guess I am just missing the bow lift needed.

All Dodge : I'll have family on my boat in a couple of weeks. I will take some GPS readings with them in the back seat and let you know how the boat changes.

Thanks!
Joe

 

[alldodge]

Look forward to seeing what you come up with

 

[Faztbullet]

Changed center of gravity???

 

[Watermann]

When searching and testing props for my boat I found there wasn't really a silver bullet that killed every issue that comes up. I found you just have to compromise with what you have going on and how you use your boat.