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Fly-By-Night
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Discussion Starter #1
Before I get 15 replies telling me I need to provide speed and RPMs, I will eventually, motor isn't even hung on the boat yet. Just looking for a good starting point. I care more abut top end than hole-shot.

Boat is Alweld 1656 2deg of deadrise weight is listed at 575 + me 230 + fuel 35ish? + battery 45ish + cooler 50ish. So in the neighborhood of 950lbs total.

Motor is 60hp 2 stroke 59ci tiller.

I am thinking 3 blade 11 1/4" 17p

What do you guys think?
 

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Premium Member
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1,906 Posts
I’m thinking a 15p is more in the ball park. 17p might not turn up the rpms.
Now, need to know rpms, speed, motor height, and weight distribution before I can advise more. SS or aluminum?
 
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Fly-By-Night
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3,128 Posts
Discussion Starter #4
I’m thinking a 15p is more in the ball park. 17p might not turn up the rpms.
Now, need to know rpms, speed, motor height, and weight distribution before I can advise more. SS or aluminum?
Stainless, motor will be high up on Vance manual JP, gotta give me more time for the other #s

Big Foot?
No it's the small 1.83 foot.
 

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Forgotten Coaster
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2,363 Posts
For apples to oranges comparison, I'm running a 13 pitch Trophy four-blade stainless on my Mercury 60 four-stroke.
 

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Fly-By-Night
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3,128 Posts
Discussion Starter #8
Ok, had some info wrong. Foot gear ratio is 1.64. I will likely be looking for a lower pitch than I orig thought since this thing is higher geared.

Got the motor hung and ran it with an ooooooollllddd alum prop yesterday evening. Prop is 10-5/8 dia 12p

Porpoising like mad even with the motor tucked. Motor is mounted pretty high (prop shaft is prob 2-2.5" below running surface. Tried to power through, that was a no go, entire boat leaving the water with throttle pinned, and continued to do so.

Adjusted (beat with hammer) the fixed tabs on the back of the boat. That helped some.

Lowered the motor some that helped a bit more.

Finally got the boat to level out at WOT but still having to run slightly neg trim. Topped out at 36-37mph.

Prop looks to have a fair bit of rake making me think it's more of a bow lift design (not what I need based on yesterday. Also it easily lost grip when the motor was higher, you could feel the boat really start to fly and the motor turn up, but then then it would either lift the bow and bounce like a bronco on meth, or lose grip.

Also motor wasn't hitting the rev limiter. Expect tach to be in today.

Think I am needing more of a cleaver/semi cleaver that can run near the surface, smaller dia, and slightly more pitch to compensate for being up high.

Any opinions welcomed, and I will follow up with more accurate #s hopefully tomorrow.
 

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Premium Member
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Post up some pics of your rig. I think your heading in the right direction though if I’m reading right.
 
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Fly-By-Night
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3,128 Posts
Discussion Starter #10
Monday evening I took a small wrench and added a bit of cup to the prop in an effort to run the motor higher without losing grip, and to see how the boat would respond. Ran the boat. No difference. Porpoising like mad at anything other than full negative trim. Damn, back to the drawing board...

Tach came in yesterday, but not installed yet. Couldn't run the boat because it was raining to beat the band here yesterday afternoon. So I just sat around thinking....

The porpoising has me scratching my head pretty hard since my motor was so high, and my go to solution for that is to keep raising a motor until there's not enough in the water to dig.

Well I went out to the boat last night and stuck a straight edge on the bottom at the transom, NOT GOOD, probably has 3/4" of rocker in 2'. This prob never caused an issue with the 30 because I wasn't going fast enough to have it really lift and I was always <30mph. But the entire bottom of the boat looks to have a slight rocker up to the rake of the bow...$H!t.

Ordered a Powertech SCB 15p, not sure when it'll be in. In the mean time I am going to massage the last 2' of hull flat to start with and see how it behaves. I will hold off on adding any hook until I see how it responds. Going to start small and test often, I figure if it starts to calm it down I'm going the right way.
 

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Fly-By-Night
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3,128 Posts
Discussion Starter #11
Forgot to mention full negative trim on this boat is REALLY negative, like -19-20deg transom is like 21deg rake to rear.
 

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Premium Member
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Would transom shims help w/ porpoising ? I’ve got a well boat where the sponson’s are raked out from the transom somewhat fiberglassed in wedges on each get to bow down Good luck
 

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I guess someone mentioned porpoising is usually caused by the hull. A "hook" hull or a concave portion will let air enter and then its dispelled and then enters again, then dispelled.

May want to put a straight edge on the bottom of the boat to ensure its flat.
 

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Fly-By-Night
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3,128 Posts
Discussion Starter #14
Would transom shims help w/ porpoising ? I’ve got a well boat where the sponson’s are raked out from the transom somewhat fiberglassed in wedges on each get to bow down Good luck
I have some small permanent tabs on the trailing edge of the running surface that I have adjusted down but I think the rocker in the hull is too much for them to overcome. Ithought about adding sponsons but I think that would just be a band-aid with the rocker I've got.

I need a flat running surface at least for the last 2 feet to keep it from robbing speed. If that doesn't help I may have a buddy weld me some sponsons.
 

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Premium Member
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Given any thought to rear splash guards to keep stern elevated? Jon boat was the worst thing I ever had for porpoising seems like that was due to a tucked up trim angle, manual trim. To flatten hull, what do you do? I’ve got sunfish I want to turn into a sneak boat , keep reading that a sun hull is lousy under power
 

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Fly-By-Night
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3,128 Posts
Discussion Starter #16
I guess someone mentioned porpoising is usually caused by the hull. A "hook" hull or a concave portion will let air enter and then its dispelled and then enters again, then dispelled.

May want to put a straight edge on the bottom of the boat to ensure its flat.
It's not flat, it has rocker (opposite of hook). I could actually benefit from a small properly placed hook in this boat with the power I am running.
 

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Fly-By-Night
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3,128 Posts
Discussion Starter #17
Given any thought to rear splash guards to keep stern elevated? Jon boat was the worst thing I ever had for porpoising seems like that was due to a tucked up trim angle, manual trim
Yep maybe, I'm going to get under there with a piece of wood and a hammer and try to get it as flat as I can then run it and see what it does.

I have power t&t on this 60 2 stroke.
 

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Fly-By-Night
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3,128 Posts
Discussion Starter #18
Ok massaged the hull with a 4lb hammer and a block of wood, on the last 2' of hull. It improved quite a bit. Still can't run much trim but I can get level with the motor (or very close).

Will wait on my new prop before I correct (beat on) the hull any more.
 
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