Prop's performance & trim tabs - need help

[Briguy]

Peter, there is a guy on the thehulltruth forum called propgods. He could recommend a stern lifting prop. I have twin 115's 4 strokes on my bracket which weigh 416lbs each. I guess they are in the ballpark of your motors. Also can you move batteries forward? I did think your boat rode bow light compared to mine for sure. Mine runs perfectly flat once i got the props dialed in correctly. I run 24" stiletto props. 4 blades may be the ticket.

[Fr. Frank]

Peter, Tim's right about motor height. You need to go as high as you can without ventilating at neutral trim in medium seas. (You shouldn't be on plane in heavy seas). That said, you've got a lot of weight hanging 2 feet aft of your true planing stern. You REALLY need sternlifting propellers.

Tim's right about which props work well, too. I would only add to consider the PowerTech SCE4, PTC4, & OFS4 props. The OFS4 is very similar to the Mirage+, but a 4 blade, and the PTC4 is similar to the REV4. The SCE4 is like the old Yamaha semi-cleaver, but even better. It's very good for high-speed running offshore in a swell, as it can run partially surfacing before ventilating. The SCE4 does sacrifice some hole-shot performance in favor of it's performance in seas.

[peterb]

Thanks for the feedback.

I believe that my two motors weigh over 450 pounds each, and when you add the bracket that is a ton of weight.

My two oil tanks are in the enclosed transom and the batteries are under the console.

I really don't care about WOT speed nearly so much as the comfort of the ride (especially since I am going offshore more now).

Brian, I saw that same add about propgods. Also they will let you test put propo I think before buying them.

Thanks again

Peter

[gw204]

A set of Mirage Plus wheel pulled the @ss end of my Grady up nicely when on plane. Made it ride like an entirely different boat.

[peterb]

Spoke to propgods. They are recoommending counter rotating revolution 4's (19" pitch x 14 and 5/8 " diameter)

What you experts think?

Also, does anyone have any leads?

Thanks,

Peter

[gofastsandman]

Powertechs are probably the best, but pricey.
Bushwacker borrowed my mirage plus and charted real time real world #s vs the his Rev 4. He killed me in hole shot, min plane , time to plane , mpg, midrange , AND TOP END.
Fr Frank, can you explain that?

Peter , I`ve been looking for a 16 p Rev 4 and there were a couple of sets of Rev 4`s on the Hull Truth about a week ago . Think they were 19s and 21s

[Fr. Frank]

Powertechs are probably the best, but pricey.

I agree with that.

... He killed me in hole shot, min plane , time to plane , mpg, midrange , AND TOP END.
Fr Frank, can you explain that?

Yes. Slip, rake/rake progression, and percentage of lift/thrust to percentage of diameter.

I went from a Ballistic 14.25"x18"P on my Merc 150, with max rpm of 5650, max speed of 44 mph, and time to plane of nearly 7 seconds, to a Mirage+ 15x17P, with max rpm of 5700, top speed of 47 mph, and time to plane of 5 1/2 seconds, to a Powertech OFS3 15.25"X16.5", with a max rpm of 6050, top speed of 52, and time to plane just under 4 seconds. In all these cases I had a nosecone and cavitation plate mounted 1.5" above hull draft.

A 4 blade prop produces more lift from the inner 50% of the blade surface diameter, and so lifts the stern more. Bow lift comes from the outer portion of the blade diameter. (Yes, you can get both from one prop)

Allow me to use extremes to make a point.
Cleaver props provide up to 75% of their lift and thrust from the inner 40-50% of blade diameter, and work best on stern-heavy boats that rely (nearly) entirely on hydrodynamic lift at speed. They use very little rake progression (change in the forward to rear angle of the blade across it's diameter) to allow for greater ventilation AND less cavitation when fully submerged.

Chopper props (big ears) work best on boats that rely on a good deal aerodynamic lift, but are still significantly water-borne at speed. These props have the highest initial rake, with any significant rake progression occurring only in the outer 25% of the blade diameter, which actually looks like extended cupping of the blade tips.

Recent developments in propellers are blending and melding of these ideas, where you get high rake 4 blade cleavers on extreme speed aerodynamic hulls, and 4 blade low-moderate rake high-cup 4 blades, which are designed to offer high performance without surfacing. The high cup allows them to be run close to the surface without ventilation, and the low rake, fast taper blade provides the needed stern lift.

Most of these recent propeller developments are really beyond my real understanding, as I have been out of the business now for 20 years. It takes a college degree in fluid dynamics and hydraulic engineering to really grasp the new stuff.

[Bushwacker]

Bushwacker borrowed my mirage plus and charted real time real world #s vs the his Rev 4. He killed me in hole shot, min plane , time to plane , mpg, midrange , AND TOP END.

My 4B prop is a 14 1/8 x 20" pitch Michigan Apollo, not a Merc Rev. 4. I was not that impressed with the Mirage +; definitely not as good as the Apollo, especially regarding min planning speed, MPG, and top end, and that was with the vent plugs in. It was even worse with the plugs out. Only problem with the Apollo is it's a little too much prop for my rig - can only turn about 5250 with a moderate load, so I need about 2" less pitch. Will probably try a Powertech once I get some $ saved up. Will post Mirage + vs. Apollo numbers here when I get a chance.

Sandy - another reason my performance numbers look better is the DFI E-Tec vs. older carbed engine! The new DI engines don't dump raw fuel out the exhaust ports, which makes a big difference in MPG, especially at low speed! You're welcome to try my 4B Apollo over at Ft. Desoto. I'll be running my 4B 14x18 aluminum Michigan Vortex, as it'll turn ~ 5600 even with a very heavy load!

[Old'sCool]

Peter, My old boat ('90 22' Whaler OR) w/225 Yam. 2S and Bennett 120's. I went from the Yam. 19" 3Bl. to a Solas 17" 4Bl. I didn't have the weight issue you have. There was better holeshot, not quite the top end, but could stay on plane at a MUCH lower speed. That was my goal as that hull didn't ride too good fast in rougher water. I know all the "experts" will project what will be the end result but, if a local dealer worth their salt will let you try multiple props and document the changes/differences in return for a sale of two props is what you need.