Prop Advice

I think you are losing bow lift with reduction off full throttle. Rather than needing to raise the rear, you need to change the fore/aft balance point. Porpoising is a balance issue that you make most noticeable when using a trim angle that the engines output cant support Number of blades on a prop dont cure balance. Different props can have different rake angles ( think angle of attack on airplane wings as example of 'rake' on a prop )
So a change from 3 to 4 blade ( or vice versa) seems to cure the problem, when really it was the change in rake that made the difference in how the boat behaved at speed. But even finding a prop with the rake that gives you less porpoising still masks the underlying issue of fore/aft balance. When you changed motors and extended hull? it caused the COG to move aft due to increase in motor weight.
Try moving stowable weight forward ( free ) to see how ride changes.
By your description I would suggest raising motor a hole or two.. ( unless prop ventilates in turns? ) If you can raise the motor, you get less overall drag and generally, less bow lift for a given amount of trim angle.
Adding some 2" - 4" set back brackets to move the motor slightly aft ( moving motor back from transom increases leverage so less trim angle produces similar bow lift at max speed ) With less overall trim needed to get max speed and good ride, the boat will not change planing angle as much when you reduce throttle. ( no transition to porpoise tendency ) This is takes more effort than just raising the motor but some boats respond very well to increased setback.
To recover some of the accel lag - adding vent holes just behind the blades lets a little exhaust gas 'slip' the prop on take off. Drill holes small, 5/16 or so to start and test. I have drilled up to 9/16 holes before ventilation starts. If you over do it, marine tex or devcon epoxy fills the holes OK.
 
Owen I had a couple of friends had same problems...They put the dole fins on.... Made huge difference and no more porpoising...
 
Well I need a spare prop so this is a great time to play with props. My 14.5X19 will still make a great spare.

I will not install trim tabs, but I may install hydrofoil but I doubt it.

I want to maximize the use of the prop first :)
 
WOT
Mercury 3 blade 14.5X19 ok but could do better 6000rpm 42mph

Turning Point 4 blade 14X19 SUCKED 5100rpm 30mph porpoising under controll but didnt have anything to compair to as I had no rpm or speed.

Turning Point 4 blade 15X15 Better out of the hole, 6200rmp (to high), still speed lose and crazy porpoising at all speeds

Turning Point 4 blade 14.5X17 here tomorrow :)
 
Sounding more like trim tabs and being careful on the beach. My old 542 Explorer porpoised like a son of a ***** until I put the tabs on.
 
Fish Assassin said:
WOT
Mercury 3 blade 14.5X19 ok but could do better 6000rpm 42mph

Turning Point 4 blade 14X19 SUCKED 5100rpm 30mph porpoising under controll but didnt have anything to compair to as I had no rpm or speed.

Turning Point 4 blade 15X15 Better out of the hole, 6200rmp (to high), still speed lose and crazy porpoising at all speeds

Turning Point 4 blade 14.5X17 here tomorrow :)
Click to expand...

That is very surprising about the 4x19 prop. You lost 900 rpm which equates to at least 4 steps up in pitch if you follow the prop charts. Does not make sense to me either. I'm sure you read the same info about that prop I did. Worked as described 2 times for me on 2 entirely different boats and others I know as well.
 
Fish Assassin said:
No it's not........ :)
Click to expand...

Tabs simply lift the stern and peg the hull and bow in to the water. Putting weight up front will do the same thing as long as you can determine what average speed you want to run at and weight it accordingly. The 15/15 blade you tried would definitely lift at stern over a 3 blade as much as you could probably expect and it does not sound like it helped at all.
 
I am not trying to drive my nose down.........

I am just trying to keep the stern higher as I drop the rpm and pop out of the hole faster.....
 
I'm thinking the laws of physics may win this one. You are trying to drive at a speed where you are bow high. Even if a 4 blade prop held the stern higher it will only do it for a very short time and short rpm range.
 
I think you will get what you want from the 17pitch. I would expect to loose a couple mph at WOT but small price to pay for no porpoise, quick to plane and ability to stay on step at slower speeds that you get from a 4 blade prop. All that said my SS solase prop is like apples and oranges to what you are buying.
 
4 blade 14.5X17 Turning Point gave me my RPM's back like I had with the 14.5X19 Mercury Prop. Popped up better, didn't porpoise well reducing my speed.(DIDN'T NEED TRIM TABS LOL :) ) I'd almost say problem solved....... BUT I lost 5-6mph WOT and 4-5mph at 4000rpm.

Going to try 3 blade Turning Point 14.5X17 and 14.5X19 in aluminum and stainless tomorrow or Friday. Ported and more ridgid props
 
I have always lost cruise speed with 4 bladed props but never had a boat with terrible prop slip, was just trying to get better hole shot and lower rpm plane speed.

Did you add a pod to this boat prior to the new motor?
If so my money says your motor is mounted to low and or you need some wedges
 
Last edited by a moderator:
I have always lost cruise speed with 4 bladed props but never had a boat with terrible prop slip, was just trying to get better hole shot and lower rpm plane speed.


My money says your motor is mounted to low...
 
Some guys actually gain top end speed with the merc rev 4 (case depending)
 
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