YAPQ- Yet Another Propping Question

[erebus]

I did some searching around and some testing and I have some results and some thoughts I'd like to throw out to the Seacraft Hive mind.

I have a 1975 18SF, which is pretty stock except for: fuel tank moved forward, batteries under the console, console itself moved forward about 6-8 inches.
Fuel tank is under deck 32 gallon.
Motor is 1998 Mercury 2 Stroke ELPTO 115 HP, 20 inch shaft (runs really good. Well maintained)
Motor is mounted 2nd hole from the top, but av plate was pretty much in line with the hull when I mounted it.
Prop is a Michigan Wheel 13.25x17 aluminum.

With me (230 lbs.) the wife (125 lbs.) full tank of gas (~200 lbs.) Plus some beach junk and enough food for a 230 pound guy, I feel like the motor is straining really, really hard to get the boat up on plane.
Almost feels like I'm dragging some dead weight.

Need to nail it up to almost 5000 RPM to get up on plane, takes about 5-10 seconds, levels off and cruises on plane happiest at about 19 kts at 4200 RPMs.
Yesterday it was nice an calm in Wellfleet Harbor so I did a full throttle test.
5400 RPMS and 27.4 kts (gps)
Looking over the stern, the AV plate on the motor is buried.
Shell fall off plane at 16 and below.

My thoughts are maybe the motor should be raised a hole or two?
Propping thoughts? I thought 13.25x17 would be just about perfect.
I have a stainless semi-cleaver style I was going to try thats 13x17. Maybe a little stern lifting will help?

Any thoughts, observations or opinions?

Thanks!

[NoBones]

Well Zach, After much deep thought you may want to consider
going on a diet... Your wife will be happier and so will
your strained 115 Merc..

OK, I had my fun..

Add trim tabs first, they will help alot !

Hopefully the prop Gods will chime in.. I have never been real
good trying to figure out what prop was best !

[erebus]

Originally Posted by NoBones

Well Zach, After much deep thought you may want to consider
going on a diet... Your wife will be happier and so will
your strained 115 Merc..

Hmm... let me think about that for a minute.
.
..
...
Ok, not a chance.
Guess I need a bigger motor/boat/cooler/swimsuit.

[NoBones]

Originally Posted by erebus

Hmm... let me think about that for a minute.
.
..
...
Ok, not a chance.
Guess I need a bigger motor/boat/cooler/swimsuit.

Zach, glad you have a sense of humor like the rest of us here!
You have to be a little thick skinned to put up with this chit...

I'm in the same boat as you, me 210 lbs, wife 115 lbs....
Why do you think I have 200 ponnies on the back of bones..

And yes, I need bigger swim trunks too.

[gofastsandman]

Originally Posted by NoBones

Well Zach, After much deep thought you may want to consider
going on a diet... Your wife will be happier and so will
your strained 115 Merc..

OK, I had my fun..

Add trim tabs first, they will help alot !

Hopefully the prop Gods will chime in.. I have never been real
good trying to figure out what prop was best !

The older I am the smarter you get. The spin is what throws everyone off.
You can also go to full powah in a jif. Ports we may not have seen.
What are your slip numbers wot?

[tautog_33]

I have a solas 14.75 x 15 pitch if your interested. I also have a stilleto bay pro III in stainless which is also 15 pitch. Both props are lightly used, my 1994 mercury 150xl 2.0 revs up past 6000 rpms with both props. I now run a mercury mirage 17" pitch and still get to 5800 rpm, i might need to buy new hub for mirage prop seems like its slipping at WOT. I'm in southeast MA let me know if your interested.

[tautog_33]

Just found this thread this on scream and fly
http://www.screamandfly.com/showthre...merc-115-elpto

I still think you would benefit from a 4 blade with a 15" pitch. Your welcome to try the ones I have.

[Old'sCool]

A 4 blade would help hole-shot but does sound like it needs to come up a hole.

[sidelock]

What is the proper mounting height for an outboard and is it the same for all v bottom boats and o/b motors ?

[Bushwacker]

Originally Posted by sidelock

What is the proper mounting height for an outboard and is it the same for all v bottom boats and o/b motors ?

The correct height is whatever it takes to get the AV plate above solid water. On a 20 SeaCraft with no bracket, that typically means the AV plate, when trimmed parallel to keel, is about 1-1.5" above keel.

Zach, I agree with advice from FS and others. Motor definitely needs to come up at least 1-2 holes; need to get the height correct before screwing around with props, and also make sure your tach is accurate. Many analog tachs are often way off!

If you're falling off plane at 16 kts with that light motor and weight moved forward, the boat is trying to tell you it needs more stern lift! A 4B prop and/or a fin will give you that. And although you outweigh me by about 60 lbs, you really aren't carrying all that much gear, so your hole shot should be much better! Less pitch and more blade area will improve that! I ran my much heavier 20' Seafari with a 1975 "115" that probably wasn't much more than 100 hp at the prop, and it would plane at 12 mph with a very heavy Bahamas cruising load including a couple of coolers, 2 weeks worth of groceries, 80 gallons of gas and a couple of 170-180 lb guys and dive gear! I ran a 13 3/4 x 15 OMC 3B SST prop that turned 5400-5700 depending on load. Ken at Prop Gods can hook you up with the right prop; I'd think a 15" pitch 4B with whatever diameter is right for your 115 to wind up to it's max rated rpm would give you the performance you're looking for.