Futura Mk3 owners: What prop/max. speed?

Northern Pike · 27 June 2013, 14:38

Trying a new motor and I don't think I've found the right prop yet. E-Tec 50 with tiller handle.
Started with a Viper stainless 13 7/8 X 17. max rpm was 5250: not high enough. Dropped to same prop, lower pitch 13 7/8 X 15. rpm.s are now higher and close to optimal. But max. speed is lower than I had hoped for, at only 26-27 m.p.h. with a light load.
What props/HP are you guys using and what speeds are you getting?

Locozodiac · 27 June 2013, 16:09

Is that sib well inflated to it's max factory recommended working pressure, well load ballanced, well trimmed and engine sits at opt transom height ? The final top speed will depend on the engine brand use and different pitch/size prop availability for that brand HP.

Which was your wot speed with standard delivered prop when at 5,250 rvs ? 27 MPH at near max wot rpm is definitely low for a 50 horse. My 430 Mt rib with a 18 HP it's doing near 22 Knots with me alone at wot.

Happy Boating

Northern Pike · 27 June 2013, 16:26

Yes, inflated, balanced. GPS wasn't working that day but it was around 25-26 I estimate. I'm up one hole. Might try coming up one more, but with previous motor up 2 holes I got occasional ventilation.

Locozodiac · 27 June 2013, 16:35

Float sib alone, trim engine to be perpendicular to boat, anticav plate must ride paralell to water surface when boat is on plane. Probaby engine sits too high on transom, prop is not biting water properly as it should at wot.

Place a mate up front, sit on tube next to transom, full throttle, once on plane pull your head out and check water flow passing through leg, do you have water splashes over or out transom ? If not. Check if water flow passes near lower anticav plate or under small upper deflector plate so to know which transom height that engine sits on.

Happy Boating

Northern Pike · 27 June 2013, 16:42

Done that. Water passes under but close to upper small deflector.

Locozodiac · 27 June 2013, 16:55

How close ? Is water flow flowing paralell to upper small def plate as in pic ? Are you testing wot on flat, no wind water conditions ? Are U using a pressure gauge to inflate sib's tubes & small speedtubes if having so ? Do you have a center cosole, or it's a plain open sib ?

Happy Boating

Northern Pike · 27 June 2013, 17:25

Yes. Flows nicer than in pic. Not so splashy.
I can see anti vent. plate somewhat.
Yes, yes, yes and yes.
I have power trim adjustability.

Locozodiac · 27 June 2013, 17:51

Water seen on posted pic is no splashy at all, it's flat churning water from slightly choppy sea when that sib/engine combo was tested. You should not be able to see anticav plate whatsoeever if water flow passes slightly under small upper plate. Would you say something like this...

Happy Boating

Northern Pike · 27 June 2013, 17:57

More like that than the first pic. Thanks!

captnjack · 27 June 2013, 18:10

While the Viper is made for V4 and V6 engines...
Try going back to the 17" pitch, but trimming the motor up more.

You need a GPS and current free water, minimal wind. Don't "estimate" speed, measure.

I suspect you are overpropped but getting ventilation and its ventilation which is confusing your rpm changes not actual changes in speed.

Northern Pike · 27 June 2013, 18:23

I have a GPS. I referred above to only one event when my batteries died.
Speed is constant, not fluctuating. If ventilating i would hear revs increase as it ventilates, and speed would drop.

Locozodiac · 27 June 2013, 18:27

Is that a standard prop factory delivered ? If not, better ask Evinrude which of their brand props, size/pitch would recommend for that engine mounted on a light weight boat ? Then going from there to a +,- pitch for best top sib/engine rpm optimization if needed. Much better than making other brands props costly purchase guessing...

Happy Boating

Northern Pike · 27 June 2013, 18:39

Yes, OEM prop as recommended in consultation with the dealer and the supplier. First tried 17 pitch, then 15 to get more rpm.

Locozodiac · 27 June 2013, 19:03

Very strange indeed, and that's not a heavy sib, with a 50 should fly to US border. That's a center console sib/engine combo, with small speed tubes under main ones, right ? Ask dealer/supplier which top speed are you supposed to achieve with both recommended props ?

With a 30 HP OEM standard prop, my 430 rib achieves 31 knots at wot. Original delivered OEM props used on light sib/rib inflatables performs top best as personally have rpm tach & gps tested.

Happy Boating

Landlockedpirate · 27 June 2013, 19:05

I had the old Futura Sport (Small speed tubes) with a Yamaha 50hp 2 stroke. Stunningly fast sib which hit just over 50mph when propped and trimmed up.

So on the face of it 25mph for yours does seem slow, however the new bigger speed tubes do make a difference and Zodiac only quote a maximum speed of 37mph with a 60hp engine.

Did you try it with the original Evinrude prop ? I'm a sucker for shiny new props but I have realised over time that the original prop can often be the best one to use.

captnjack · 27 June 2013, 19:27

Quote:

Originally Posted by Northern Pike

Yes, OEM prop as recommended in consultation with the dealer and the supplier. First tried 17 pitch, then 15 to get more rpm.

The SS viper is NOT the standard prop for that engine. Its made for V4 engines in the 75-140hp range. For much heavier ~24ft cruising boats to run in the 25 mph range.
# 389949 V4 SST II 13.75 x 15. For 22-26 ft. Cruisers

I'm surprised its working for you on a 50hp Etec at all.

I would go back to a standard 3 blade ali prop, no cup, no rake, and figure out performance at that baseline before messing with alternatives. You are overpropped, but its not a question of pitch which is roughly correct. The incorrect blade shape is screwing you up and slowing you down.

Northern Pike · 27 June 2013, 20:15

Quote:

Originally Posted by Locozodiac

That's a center console sib/engine combo, with small speed tubes under main ones, right ? Ask dealer/supplier which top speed are you supposed to achieve with both recommended props ?

Its a tiller, no console. Yes, Zodiac Futura Mk 3 has speed tubes. Dealers no nothing about inflatable boats.

Northern Pike · 27 June 2013, 20:31

Quote:

Originally Posted by Landlockedpirate

So on the face of it 25mph for yours does seem slow, however the new bigger speed tubes do make a difference and Zodiac only quote a maximum speed of 37mph with a 60hp engine.

Did you try it with the original Evinrude prop ? I'm a sucker for shiny new props but I have realised over time that the original prop can often be the best one to use.

Yes, Zodiac spec.s 37 mph max. for this hull. I should be able to come closer than half with max. recommended HP (50) don't you think?
60 is max. allowed.

This is a brand new motor and prop. I started with a best guess according to dealer, factory rep., and my experience. I think we are in the ballpark when it comes to pitch, but I think the larger diameter is my problem.
This motor has the same large gearcase as the bigger ones mentioned by capnjack, so available props seem to be a little large when it comes to diameter.
A stainless prop was included as part of a promotion. I thought that was a great bonus but so far the first 2 I've tried haven't worked as well as I had hoped.
I've been thinking about aluminum too lately, but since I've got a stainless one coming to me, I had better settle on one of them first. I can always sell it and buy 2 aluminums.
Thanks for your help guys.

Landlockedpirate · 27 June 2013, 21:05

Quote:

Originally Posted by Northern Pike

Yes, Zodiac spec.s 37 mph max. for this hull. I should be able to come closer than half with max. recommended HP (50) don't you think?
60 is max. allowed.

.

Yep, you should be getting a bit more, 33-34mph ?

I love the Etec, we had a 90hp on a centre console and it was fantastic. As everyone has pointed out the SS props you are running are way too big, look for a prop with a 11-12" diameter and stick with the 17" pitch. Propping boats is a bit of a black art but I would find out what the standard ali prop supplied on the engine is and get one of those.

Its not perfect and you have to use a rib rather than a sib but I always start with this prop calculator:

Prop Selector | Mercury Marine

Have just run it making some assumptions for your boat and it suggests 33mph with a 11x17 3 blade aluminum, I guess I wasn't too far off

captnjack · 27 June 2013, 21:27

Quote:

Originally Posted by Landlockedpirate

Have just run it making some assumptions for your boat and it suggests 33mph with a 11x17 3 blade aluminum, I guess I wasn't too far off

^^^^^^
Ding!!! Diameter and blade shape/area/size are just not right for this motor.

There might be another SS prop that works well, but its not going to be in the viper product line.