Hello from the old continent,

I have a 1977 Martini 26 x 7ft. Non steps, Non pad. Typical hook from that era. Bare hull, empty bow. 3.200≈3.800 pounds.

I run a 465HP 1992 502 (Blue engine). Thru-hull Gil exhaust. Holley 800. All stock.
Bravo I 1.65 17≈17.5 X. Dimension.

I try two props:

- Bravo I 28p. Sharpened, but not fresh. And unbanlanced. The boat runs great attitude, but over 50MPH. Bow goes down. (No porpoising, no chinewalk)

the prop is not true. Slip numbers are high:

28 1.652.200 25 29%

3.000 35 27%

3.500 42 25% (Pre-secondaries point)

4.600 58 22%

4.900 62 21% (WOT)

- Mirage 27p stock. Good condition. The prop blows out at 25MPH. I have to go back from plane. No way overpass 25MPH gap. (Too high X dimension)

I have now the opportunity of purchasing a 26p Bravo I lab finish, mint condition.

my targets, in order are:
1.- lower my slip as closer as possible to 10%.
2.- reach 5.200≈5.250 RPM
3.- keep bow attitude at WOT.

Im worry if the 26p lab and mint, will give me too much RPM in comparison of my 28p lazy prop.

Soo I want to listen your always smart suggestions.

maybe Bravo 27-28p Lab or Hydromotive Q-IV?

thank you folks.

I can provide some input of just my testing (messing around) over the years. Lab finishing props varies greatly. But usual rule of thumb is 200-250 rpms on a higher x dimension per inch pitch change. I.e. 26-28 I would expect you to gain 400-450-500 rpms (tach's also greatly vary).

I have never had success with a Hydromotive quad 4 being able to plane above 4.5" below. Obviously every boat is different but once I started getting into the 3-4" under the bottom they were not useable in a 4 blade. P5x or Bravo 4 blades excelled here.

3 Blade Mirage/Mirage + are usually DONE around 5" under the bottom. Work well the deeper the drive. Magic for them is 5-7" under. You are likely near 5" under with your measurements (likely 17" XD has you about 4.865" under) which would tie to the fact it seems you can in fact plane with a 3 blade but cannot run with it fully. Likely you are teetering right near the magic all done of 5". I would suggest trying 2 new props. You could also try a .25" spacer in the drive and play with the 27p Mirage/Mirage +. But the higher the faster so proceed with 4 blades for now.

It's been a long time since messing with an hp500 502 carb motor or a 420 merc 454 but I believe 5300 was the right max RPM for those motors back then. Being where I * think * your X Dimension is you could certainly try to run a Hydromotive Quad 4 as well as a Bravo 4 blade. The bravo stated pitch unless labbed to a true pitch is usually .7 off. I.e. a 26p stamped bravo for slip calcs stock would be 25.3 pitch. Hydromotives are true pitch and finding a stock one of those in a 23-29p seems harder and harder. Ton's messed with. Make sure and try a non messed with full width one without a diffusor ring added.

You were about 21.25% slip on a 28 1.65 gear with 4900 rpm. Knowing what we know dropping 2 pitch sizes you would likely be running into the rev limiter on the 26. My wager is likely see about 67-68 around 15% slip. Usually when you are without a notch or pad and around 4.8" under 10-15% slip would be your targets. The more prop slip, the longer your drive will last but dialing the combo in is the fun part (to some). If you can get near 12% slip on 4 blades you are in the right direction. Try and find a 26p Hydromotive stock quad 4 and a 26p bravo 4 blade. Get above 67 mph and we are heading in the right direction. You will want to play around to find a prop that ideally with a full tank of gas allows you to get to 5100-5200. With some chop/lighter fuel you will gain the rest. I think for your situation a Hydromotive Quad 4 in a 26 or 27p will be your friend that is bone stock/not messed with to get a baseline off.

I have been playing with a very similar x dimension on a small pad Apache 22' 680 hp BBC and at 5" under a Hydromotive Quad 4 works WONDERFUL (albeit in a 29p).

Thank you for all your information, you give good ideas of how to continue.

I will try to find a 26-27 hydromotive or maybe I will send the 28 to Germany to rebalance it and give it a true 28 pitch.

What do you mean by typical hook??? Hook will reduce bow lift and scrub speed. How much hook in the last 4 feet or 1 meter???

You do not want to use a Hydro Q4 prop on your boat. It will lift the stern and not carry the bow.

You want to spin your engine to 5200-5300 rpms to get the best performance.

Your best prop will probably be a custom labbed 26 Bravo with extra cupping and rake added.