AllDodge

iTrader: (1)

There is a 2002 boat test which list its best cruise at 3400 rpm at 34.4 and getting 2.12 mpg, and top speed at 70 mph
https://www.boattest.com/oem/386/boats/138/0/

Another 2015 but obtained numbers from Formula showing with 350mag getting 62 to 65 mph and 377 with 3 mph increase. Best cruise at 4000 rpm and getting 49 mph. Also noted if it had 8.2 motors the balance would be thrown off
https://www.boattest.com/review/form...41_292-fastech

On Formula forum there is a 312 and 292 with porpoise issue and member fossil fuel mentioned to have the props turn out instead of in to help
2 Fastech Questions... Extension boxes? Ladder?

Anyone got a 311 that doesn't porpoise???

phragle

iTrader: (3)

hows the bottom of the hull?????

AmiableDave

BB.... I was thinking the same thing. Drive spacers, five blades. Along with a longer tube diffuser ring or extension boxes. The latter being the last resort.

Dodge..... Thanks for the links. The closest was the 2015 review. But there figures make best light of the boat. For instance, the 7000 lbs weight to HP ratio is false. The 7000 lbs is dry weight. Plus Formula changed to a 97 gallon gas tank removing the 113 which I have.

Finally the boat looks like it came of the show room floor. So the bottom looks like a new born baby's ass...

BBYSTWY

I think he was saying like is there a hook in the bottom rather than if it's clean..from what I've read I believe a hook can and will cause these issues

Griff

It doesn't really work that way. Slip is not wasted thrust. It really doesn't take hardly any hp to spin the prop if its slipping. If you reduce your slip, most likely your rpms will go down when the same amount of throttle is applied.......which is not the same as running at the same rpms. You are thinking that reducing slip is linear with speed and by reducing slip, it will automatically increase speed by the same percentage. If you decrease slip, it will create more load and reduce rpms.

Look at it this way.....Which one is better??? Assume they have the same cruise rpms and speed and handle equally well
Prop 1 runs 72mph at 5000rpms with 22% slip
Prop 2 runs 68mph at 5000rpms with 12% slip

Which one is better???

Mentalpause

I'd call Brett. BB can tweak the props to give you more stern lift. Not sure if they have a diffuser ring on them or not, but a diffuser ring will also give you more stern lift. But that doesn't mean your props will be more efficient, it just means you will get more stern lift and possibly be able to trim out a little at cruise. It is pretty common that if you over trim your prop slip increases. Obviously your current set up doesn't like much if any trim at 40mph. That's not necessarily a bad thing. What is your slip across other RPM readings.

AmiableDave

Griff, Your last makes sense. I just know the boat can be set up better. Its the how, with out spending a small fortune that's got me scratching my head. Don't get me wrong. I don't mind spending money if it ends in success.

Mentalpause, Brett will be called at a later date. There is a wealth of knowledge here. If someone comes up with a worthy idea that I can do, I'll do it first. With WOT 5000rpm, the slip goes to 13%. But twin stepped hulls are most efficient at high speeds.

AllDodge

iTrader: (1)

I know you don't want to carry the extra weight, but have you ever filled the water tank and tried a run?
If not maybe ask the wife if she would go to the bow to see what happens, do note that if wife goes to the bow, its more in the bow and less amidshipsgallons
The 19 extra gallons of gas 114 pounds

Griff

Do you have any pics of the boat running at cruise speed??? Then we could see if it looks like its running too wet.
That amount of fuel is not helping your slip numbers at all. That much fuel will also change the running attitude of the boat. My boat is night and day different with full tanks and 1/2 tanks.


Your slip numbers really are pretty normal at 17% at cruise and 13% at WOT. You might be able to get them down a couple % with some prop tweaking.
Although you have a stepped hull, Fastech's are still not extremely efficient and the 292 had its quirks with needing the 1.65 drives to run best and being somewhat slow to get on plane.

Knot 4 Me

Yeah I'm not sure why you always run with a full tank. My last boat was night and day difference running at 1/2 tank vs. full. Felt like a completely different hull and that I gained 100 HP.