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Author Topic:   Thoughts on prop for 60HP Bigfoot on 150 Sport
Moe posted 08-26-2003 12:29 PM ET (US)   Profile for Moe   Send Email to Moe  
I've spent a good deal of time with Merc's Prop Selector, and
have been gathering data on this subject, so I thought I'd
put this out there for those who're researching the same
thing. In fact, 60HP 170 owners may find something useful.
May save someone else some time.

From what I gather, the BigFoot is limited in prop choice to
a few special Black Max props if you don't want to experience
clutch rattle. The manual says it's okay to use other props
and they won't affect durability, but just sticking to the
Mercury recommended Black Max props, here's what I found.

The 264 lb, 995cc/4-cylinder/4-cycle BigFoot EFI 40, 50,
and 60 HP motors have the same beefy (hence higher drag)
2.33:1 lower end as the carbureted 75 and 90 hp, 303 lb,
1386cc/3-cylinder/2-cycle and 386 lb,
1596cc/4-cylinder/4-cycle motors (that's four 75/90 motors).

Besides drag, the larger 2.33:1 BigFoot lower end adds
16 lbs compared to the 1.83:1 "small foot" 248 lb,
1000cc/4-cylinder/4-cycle 50 and 60 HP EFI motors, not
available on the 150 and 170 Whalers.

The 264 lb, 995cc/4-cylinder/4-cycle BigFoot EFI 40, 50,
and 60 hp motors are 45 lbs heavier than the 1.64:1 "small
foot" 50 and 60 HP carbureted 219 lb, 966cc/3-cylinder/2-cycle
motors, like the 60 HP standard on the 150 Sport Whaler.

So the 60 HP BigFoot EFI, optional on the 150 Sport and the
170 Montauk, has the same prop shaft rotational speed as the
carbureted 75 and 90 HP motors (be they two or four stroke),
with only 80% of the prop shaft torque of the 75 HPs, and 67%
of that of the 90 HPs, in the max HP rpm range. Other props
designed for the larger "foot" of the 75 and up motors, which
fit the BigFoot, all seem to have too much pitch for its
lower HP (and hence prop shaft torque).

On the other hand, it has 70% of the prop shaft rotational
speed, and 142% of the prop shaft torque as the 60 HP
"Classic" two-stroke, standard on the 150 Sport, in the max HP
rpm range. Based on this, the 15" pitch prop on the 60 HP
BigFoot EFI should equate to a 10.5" pitch prop on the 60 HP
two-stroke (if diameter isn't a factor and slippage is the same).
However, I suspect diameter IS a factor, and the 15" pitch with
near 14" diameter on the 60 HP BigFoot is more equal to a 12"
pitch with 10-11" diameter on the 60 HP two-stroke

It doesn't seem that the "Fiberglas Fishing boat" is a good
match to the 150 Sport with this motor using Mercury's Prop
Selector. The "Flats Fishing boat" seems the closest fit.


When set for Flats Fishing boat, Overall good performance:

For a boat weight 1760 lbs and below,
it can't find an appropriate prop.

For a boat weight between 1761 lbs and 2233 lbs,
it recommends the 15" prop
for 35.9 mph and theoretical pitch of 16.9" at 1761 lbs and
for 31.8 mph and theoretical pitch of 15.0" at 2050 lbs and
for 29.6 mph and theoretical pitch of 14.0" at 2233 lbs

For a boat weight between 2234 lbs and 2675 lbs,
it recommends the 13" prop
for 29.6 mph and theoretical pitch of 13.9" at 2234 lbs and
for 27.7 mph and theoretical pitch of 13.0" at 2420 lbs and
for 25.4 mph and theoretical pitch of 12.0" at 2675 lbs

For a boat weight between 2676 lbs and 3000 lbs,
it recommends the 11" prop
for 25.4 mph and theoretical pitch of 12.0" at 2676 lbs and
for 23.3 mph and theoretical pitch of 11.0" at 2950 lbs and
for 22.9 mph and theoretical pitch of 10.8" at 3000 lbs

At 3001 lbs and up, it reports the power to weight ratio for
these options is too low for its mechanical propellor selector.


When set for Flats Fishing boat, Quick planing:

For a boat weight 1666 and below,
it can't find an appropriate prop.

For a boat weight between 1667 lbs and 2122 lbs,
it recommends the 15" prop
for 37.5 mph and theoretical pitch of 16.9" at 1666 lbs and
for 33.3 mph and theoretical pitch of 15.0" at 1940 lbs and
for 30.9 mph and theoretical pitch of 14.0" at 2122 lbs

For a boat weight between 2123 lbs and 2546 lbs,
it recommends the 13" prop
for 30.9 mph and theoretical pitch of 13.9" at 2123 lbs and
for 28.9 mph and theoretical pitch of 13.0" at 2300 lbs and
for 26.5 mph and theoretical pitch of 12.0" at 2546 lbs

For a boat weight between 2547 lbs and 3000 lbs,
it recommends the 11" prop
for 26.5 mph and theoretical pitch of 11.9" at 2547 lbs and
for 24.4 mph and theoretical pitch of 11.0" at 2800 lbs and
for 22.9 mph and theoretical pitch of 10.3" at 3000 lbs

At 3001 lbs and up, it reports the power to weight ratio for
these options is too low for its mechanical propellor selector.


Looking at boat weights, using the Flats Fishing boat numbers:

With 2 X 150 lb persons, 100 lbs of gas, 100 lbs of gear and
options, and the roughly 300 lb 60 HP BigFoot motor a 900 lb
150 Sport comes out to 1700 lbs. This is at the lightweight
end of the Quick planing for the 15" prop, which should yield
36-37 mph according to the prop selector. This is close to
Clark Robert's Speed Potential Formula, which gives 37.6 mph
for 60 HP over 1700 lbs with a 200 hull factor.

However, that's what the Prop Calculator predicts for 6000 rpm
with NO slip, and there will be at least some. Even with an
additional 240 lbs of people/cargo, where we are often loaded
on our 150, 1940 lbs is at Mercury's theoretical match for
Quick planing with the 15" prop, where the predicted speed is
33.3 mph. This aligns with the Prop Calculator's result when
9% slip is used.

At maximum capacity, a 900 lb 150 Sport, with 300 lb motor,
and 925 lbs of people, gear, and gas, comes out to 2325 lbs.
This is at the heavy end of Overall good performance with the
15" prop, and where there's a theoretical match for Quick
Planing with the 13" prop, which should yeild about 28 mph.

I know that the Mercury site, and all the posts from
experienced Whalers here, say that the 2" pitch difference
should raise rpms about 400. But that's not the way the
numbers work out. 15"/13" is 1.154. If the current max speed
with 15" prop comes at 5200 rpm, then switching to the 13"
should bring it to 6000 rpm at the exact same boat speed,
assuming slippage doesn't change. If current max speed is
higher than 5,200 rpm with the 15", the 13" should be over
6,000 rpm using this factor. Perhaps there are other factors
that limit rpm at max speed (i.e. huge prop diameter), but
here's what concerns me more.

If the rpm at which the boat just holds plane well with the
15" is 3300 rpm, switching to the 13" should increase that
1.154 times to 3800 rpm. That's definitely NOT what we want.
At the speed where 4200 rpm (70% throttle) occurs with the 15"
prop, the 13" prop should turn the engine 4800 rpm (80%).
We don't want this either.

Finally, some thoughts on raising the motor. Whaler ships
the 150 with the huge BigFoot anti-cavitation plate right at
the bottom of the transom. With its much flatter stern (and
shallower draft), this puts the prop higher in the water than
the same motor position on the more deep-V sterns of earlier
models. This may indicate the motor might NOT need to be
(or shouldn't be) raised. See:
http://www.engr.udayton.edu/staff/lriggins/Whaler/comparo.jpg

From what I've seen in chop on Lake Erie, I wouldn't want the
prop any closer to the surface than Whaler put it. Keith
Shoaps (kshoaps) found that the prop ventilated too easily,
and put the water intake too close to the surface, with the
motor raised one notch. And he didn't get much, if any,
speed increase from doing so. That's what I'd expect.

The bottom line is that the stock prop, with the motor mounted
where Whaler puts it, may be about as good as it gets for the
time being... unless Merc comes out with a stainless one with
14 and 15" pitches. Just going to stainless with a 15" prop
may give the additional rpm to hit redline when lightly loaded.

If I've made an error here in logic or math, doesn't hesitate
to post a correction. Other thoughts are very welcome.
--
Moe

Bigshot posted 08-26-2003 12:36 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
All that and you want OUR thoughts :)
Jamie 20 outrage posted 08-26-2003 10:49 PM ET (US)     Profile for Jamie 20 outrage  Send Email to Jamie 20 outrage     
Is there a Guiness record for longest post in the world?
Moe posted 08-27-2003 01:01 PM ET (US)     Profile for Moe  Send Email to Moe     
I was hoping for a little more intellectual discussion ;-)

Continuing the thoughts on this...

Merc's Prop Selector and real-world experience seems to indicate
the 15" Black Max prop is capable of negative slip. Not! The
reality must be that the pitch is greater than the published 15"
at the speeds expected with this setup.

quote:
Mercury's Prop Selector results from above:
For a boat weight between 1667 lbs and 2122 lbs,
it recommends the 15" prop
for 37.5 mph and theoretical pitch of 16.9" at 1666 lbs...

Using Jim Hebert's most excellent Prop Calculator,
37.5 mph with 2.33:1 and 15" prop is -2.5% slip at 6,000 rpm!
OTOH, plugging Merc's theoretical pitch of 16.9 in with 9% slip
results in 37.5 mph!

quote:
More Merc Prop Selector results from above:
for 33.3 mph and theoretical pitch of 15.0" at 1940 lbs...

Plugging these into Jim's Prop Calculator, at 6,000 rpm, results
in 9% slip. Looks like 9% is what Merc's Prop Calculator uses for
Flats Fishing boats in this weight range.

quote:
Keith Shoaps 150 Sport w/60HP w/15" prop from
http://continuouswave.com/ubb/Forum4/HTML/001866.html

...gets me 35 mph (gps) at 5600 rpm with full up tilt.


Using Jim's Prop Calculator, this indicates -2.5% slip with
2.33:1 and 15" prop. The exact same negative slip number as
plugging Mercury's 37.5 mph in with 2.33:1 and a 15" prop at
6,000 rpm! OTOH, with 5600 rpm, 9% slip, and 35 mph plugged
into Jim's Calculator, it calculates a pitch of 16.9", same
as Mercury's theoretical pitch of 16.9" at 1666 lbs!

Consistency!

quote:

Hugh McMillan's 170 w/90 HP w/2.33:1 and 15" aluminum
prop from
http://continuouswave.com/ubb/Forum5/HTML/000107.html
does a little better if his reported juggling of paper in
the breeze didn't affect the readings.

Without trimming the motor WOT was 5,500 RPM and 36.0 MPH
but if I trimmed the engine carefully it would max out at
the higher numbers of 5,600 RPM and 37.1 MPH.


These results indicate a slip of -7.4 and -8.7 respectively
using Jim's Calculator with 15" prop. But when 16.9" is
used as the prop for 36 mph at 5500 and 37.1 mph at 5600,
Jim's Calculator reports 4.7% and 3.55% slip, respectively.

Using Merc's Prop Selector for Flats Fishing boat and
Quick Planing, for the 170 Montauk, with 2500 lbs weight,
90HP four-stroke w/2.33:1, calls for a 17" Black Max prop
with a theoretical pitch of 17.0" yielding 37.5 mph.

Plugging 6000 rpm, 2.33:1, 17" pitch and 37.5 mph into Jim's
Calculator yeilds a slip of 9.5% at this weight. Using 9.0%
slip and calculating for pitch yields 16.9".

All these, Merc's calcs, Keith's and Hugh's reports, seem
to indicate the pitch and slip that should be used when
calculating top speeds for the 2.33:1 and 15" prop should
probably be 16.9" with 9% slip.

This MIGHT be an alternative for the 150 Sport owner
with the 60HP Bigfoot who wants a bit more speed. Not sure
about the clutch rattling with non-Bigfoot props the owners
manual mentioned. Also not sure what this will do to max rpm.
My guess is that it might remain the same, but I haven't had
time to research what it does for 170 owners. $440 (retail)
is a lot to spend to find out. Would be cool if a 150 owner
with a GPS (not me yet) could borrow one from a 170 owner
for testing.

--
Moe


Moe posted 08-27-2003 01:11 PM ET (US)     Profile for Moe  Send Email to Moe     
Oops! There's a paragraph missing from before the last one that begins with "This MIGHT be..." Something happened in the copy and paste, and the last paragraph doesn't make sense without it. Here it is:

What's interesting is that if we change the Merc Prop
Selector for Hugh's boat above, from Quick Planning to
Durability, there are 3 stainless props recommended for
a theoretical pitch of 19.4" at 37.5 mph and for the
Vengence, the recommended is an 18" pitch, an additional
inch. Coincidentally, Whaler provides an additional inch
in stainless (16"P w/13-1/8" diameter PN 48- 16986A46) vs
the aluminum 15" with the 90HP 4-stroke 170 Montauk.

Sorry 'bout that. Wish we could edit posts!

--
Moe

Moe posted 08-28-2003 05:09 PM ET (US)     Profile for Moe  Send Email to Moe     
I might have found today why the BigFoot owners manual talks about rattling with props not designed for the BigFoot. There's a Flo-Torque III hub used on them. The hub kit for them is PN 835257K 9 ($41.00) and it says it's for 40-60HP FourStroke Bigfoot AND 90-115 FourStroke aluminum or stainless steel props, reduces prop rattle.

At any rate, this may open up use of more props without rattling, but most of the 90-115 props have too much pitch anyway.

Just another tidbit of info for this thread.
--
Moe

Peter posted 08-28-2003 08:27 PM ET (US)     Profile for Peter  Send Email to Peter     
Everytime I've used the Mercury prop selector, plugging in appropriate data for both a 22 and 15 foot Whaler, it has always suggested a propeller pitch that I know would make my engines overpropped based on the performance I currently get with a real (non-Mercury) propellers of lesser pitch. Leads me to believe that one inch of Mercury propeller pitch is not the same as every other manufacturer's one inch of pitch.
Moe posted 08-28-2003 10:57 PM ET (US)     Profile for Moe  Send Email to Moe     
Interesting... thanks!
--
Moe
Peter posted 08-28-2003 11:29 PM ET (US)     Profile for Peter  Send Email to Peter     
Comparing apples to oranges -- I have a Yamaha 70 on a 15 Super Sport. I believe that the Yamaha has the same 2.33:1
"Big Foot" gear case. I am running a 19 inch Yamaha propeller to the maximum WOT engine speed of 6000 rpm.

With a 60 hp on a 150 sport, your ideal propeller should be in the range of 15 to 17 inches of pitch. A propeller with 15 inches of pitch will probably be your best all-around propeller. According to the prop calculator here, at WOT both my 15 and 22 Whaler's yield approximately 6 percent slip.

Moe posted 08-29-2003 12:43 PM ET (US)     Profile for Moe  Send Email to Moe     
Peter, I was pretty interested in the thread you guys had going on aluminum vs stainless, and I looked up the specs on your 70HP 2-stroke Yamahas. I saw the 2.33:1 but wasn't sure you guys had the BigFoot on the 2-strokes, since Yamaha also sells a high-thrust 4-stroke.

I don't think the 60 HP 4-stroke EFI on a 150 could pull much more than 15", at least at the 13-3/4" diameter, unless VERY lightly loaded. You 15 Classic/70HP guys have a lot better HP/weight ratio, and a lot less beam in the water at the transom when on plane.

When we got interested in the 150 and EFI motor, all I wanted was a 30 mph boat. Ride and stability were a lot more important than speed. Jim Hebert's Prop Calculator said we should get about 30 mph at 90% throttle (5400 rpm),
with the 2.33/15" BigFoot and 9% slip. I suspected that's about the best max rpm we'd be able to turn with our normal load (which not surprisingly crept up to about 700 lbs from my 600 lb estimate), if I stuck with a prop that wouldn't overrev with a solo light person in the boat, especially in salt water. That was okay with me.

I'm pretty pleased with the indications from others that the 15" prop is performing like a 16.9" with 9% slip, not from the the perspective of higher speed which some owners may want, but for the lower rpm at a given speed (I drive a diesel :) ) Its axles are 3.73:1, and I find it interesting that going from a 15" to 13" prop is like taking those axles to a whopping 4.30:1!

I think BW is doing a pretty good job of propping the new Classics for all-round use. WRT the Montauks, it looks like they're now shipping an 18" stainless prop, which is more inline with the Merc recommended for 2.33:1 vs the 16" stainless they used on early 170s with the 90HP four-stroke. Could be the earlier 90 FS used 2.07:1, like the 115, and the new ones are 2.33:1, which would dictate a switch to 18" from 16".

I work on a team that does land speed racing, and you might find it interesting that we deal with the same kind of slip numbers on the salt that we do with props here.

Thanks again for your input. It's great to crunch numbers, but there's no substitute for experience.
--
Moe

elaelap posted 09-02-2003 10:40 PM ET (US)     Profile for elaelap  Send Email to elaelap     
More apples compared to the same orange: Old '71 Katama 16/17 with bottom paint; fishing gear and one downrigger; 50 lbs of salmon weights in the bow locker; 6 hp Johnson Seahorse kicker on the portside transom and about 5 gallons of gas in a six gallon tank under the console; 50 hp Yamaha High Thrust (same gearing as Bigfoot, I believe) four stroke (245 lbs) running a 13" pitch aluminum prop -- 30 mph at 5900 rpm WOT/GPS on a good day...best was 30.5 at 5900 rpm before I put on the kicker (which I never use, which gets in my way when I'm fishing or getting my fishbox cooler out of the boat, which is old and unsightly, but which just might get me home one day...).

Tony

Moe posted 09-03-2003 02:08 PM ET (US)     Profile for Moe  Send Email to Moe     
Thanks, Toni. That's useful info, especially about how high in rpms the 13" lets the 50 HP turn. Sounds like a perfect setup for ya.
--
Moe

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