Reply With QuoteNever dealt with that problem on a boat of that length, but sounds like maybe your motor is too high....may help to play with the motor height. Might try screaminfly.com for more outboard help!
That constant bouncing is driving me nuts. I can drive thru it...but then I really only have 2 speeds. Slow and trimmed almost all the way down...and wide open and trimed way up.
The prop I have is a 22 pitch stainless thru hub dog ear. I don't really know what brand. There are no markings on it.
The boat is a Stratos 18' Tunnel Vee, with a 175 Mariner.
Is there a jack plate adjustment that will stop the mid speed propoise? What other adjustments can I do to calm down the porpoise?
Suggestions?
Never dealt with that problem on a boat of that length, but sounds like maybe your motor is too high....may help to play with the motor height. Might try screaminfly.com for more outboard help!
If it's anything like an outdrive, leave it down to start. Trim up until it porpoises, then trim down until it stops. Porpoise at speed is a function of being "over-trimmed".
You could easily have too much prop there. What is your WOT RPM?
Over 5k rpms.
I used to have the same problem on my 21 foot v-bottom sterndrive. I bounced around a lot at mid-throttle. I tried to move weight around, but the best solution were Bennett Trim Tabs.
By the way, there are thousands of those minitrucks running around here in the Philippines, converted to LHD. I even made a jetboat using a supercharged F5A engine.
Over 5k rpms.
You might want to try a smaller prop, perhaps 19p, or so. You should prop so you get around 6K WOT.
My boat does the same thing with three people in it but doesn't do it when it's just me or me and someone light. The prop is trying to lift the bow but if the boat is too heavy, the prop won't be able to hold it up there. The solution is to send more water past the prop (lower pitch) or run a prop with less bow lift.
I'm jacked well above the pad with my prop shaft (about 1.75") and I could trim up so I can't see over the bow, if I wanted.
On a tunnel I would guess it is a balance issue. How much set back do you have?
I had a tunnel that the bow was so light you could pick the boat way up in the air by the sponson. But I sat way up in the front... I would porpous like normal tunnels do. I would fly the bow really high (must be careful of head winds) and it would slow to a slow lope.
Oh yes, I also changed to a straight back prop (cleaver) as the round ears tend to lift the front end high.
You know what's funny? I have posted this same question on 2 other boards, and I can't believe how many different answers I have gotten. From boat is too heavy to add weight to the front. Prop is too small and need a bigger prop. Jack up, Jack down.
I guess it is just going to be trial and error.
I measured my setup and I was 2.75" lower than the pad with the center line of the lower unit...so I raised it 1". I figure this change will be fine since I have almost 20" between the pad trailing edge and the lower unit leading edge...because the boat has a built in setback on the transom and I am running a 6" jack plate.
I guess the biggest thing I need to know is a base line to start with. like what is the OEM recommendations for the prop size...where can I get this type information?
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