Help With Porpoising

[jackreno]

I have a 3.3 Rib with a 30hp motor, I also have a sport hydrofoil on motor and it keeps my rib from porpoising when I am in boat by myself at all speeds but when my wife gets on board and sits in front we cant get max speed because the boat will porpoise, if she sits in back with me we can get max speed if I play with the trim but unable to if she is in front.

So with that said will a 4 blade prop help with this or ??, its a small narrow boat and best she stays in front.

[jonp]

I put a 4 blade prop on a boat for the same reason which made no difference to porpoising. A set of trim tabs fixed the problem.

Jon

[jackreno]

Originally Posted by jonp

I put a 4 blade prop on a boat for the same reason which made no difference to porpoising. A set of trim tabs fixed the problem.

Jon

Did the 4 blade hurt your top speed by chance, I would like to try the trim tabs but I don't have much room in back, this is a narrow rib.

[HDAV]

Quite a big motor for a 3.1m what's the layout? Centre console? Do you have adjustable trim on motor ?

[jackreno]

Originally Posted by HDAV

Quite a big motor for a 3.1m what's the layout? Centre console? Do you have adjustable trim on motor ?

Yes its one of the smallest RIBs that can handle 30hp, its a 4 stroke with trim adjustments, like I said above by myself the boat is fine and I do have a hydrofoil on motor but when my wife rides along I cant control the porpoise at top speed, gets out of control.

Here is a pic of what it looks like

[jonp]

The 4 blade Solas prop did knock back the top end speed but it increased the low planeing speed and hole shot (take offs). It was on a bigger boat which helped keep the boat at a more constant speed when working big swells. I dropped back pitch sizes with the 4 blade from a 17 to a 15 to keep the same rpm.

I recently fitted some Bennett self levelling trim tabs to my rib which gave adverse problems, but they have worked great on other boats I've owned. Maybe get some L shapped brackets made to fit the small area where you can fit them.

[Last Tango]

Hi

Firstly....I'm not having a go at your wife....The reason for the porpoising is the centre of gravity has moved too far forward of the leading edge of the wetted surface of your hull which, with a 30 on a boat this size, will be pretty close to the stern. If standard trim, and weight redistribution won't sort it, my next move would be to see if the engine can be raised any on the transom. That would reduce it's tendency to lift the bow. If you go too far it'll ventilate but there might be some scope there.

[Gilly111]

How fast do it go wene running right

[9D280]

I guess the other way of looking at the situation - is your wife as much of a speed addict as you? if not, just don't open the throttle so far when she is aboard?

If she wants the vmax, then would removing the hydrofoil from the motor help when you are 2 up?

[Poly]

The bow is not an ideal, especially comfortable or particularly dry place to sit on a small boat anyway, can't she just sit beside you at the back since it sounds like it is fine then?

[jackreno]

Originally Posted by Gilly111

How fast do it go wene running right

34 mph top speed by myself but can only do 27 mph with wife in front before it porpoise's, can reach 32 mph with her sitting in back no porpoising but the bow does ride high.

[HDAV]

Originally Posted by jackreno

34 mph top speed by myself but can only do 27 mph with wife in front before it porpoise's, can reach 32 mph with her sitting in back no porpoising but the bow does ride high.

If she is sat with you can you not use the trim to bring the bow down?

[jackreno]

Originally Posted by Poly

The bow is not an ideal, especially comfortable or particularly dry place to sit on a small boat anyway, can't she just sit beside you at the back since it sounds like it is fine then?

Yes she has sat in back but this is a narrow boat and we like elbow room when boating.

I am going to order the Propulse 4 blade prop so I can change the pitch on the go and see what a 4 blade can do for now, I am running 13 pitch 1 on boat but runs better with 12 pitch 2 on boat.

If this don't work than I guess this is just the nature of this boat being its only 11 ft long, wife is OK at slower speeds but its also nice to open it up and fly sometimes.

[jackreno]

Originally Posted by HDAV

If she is sat with you can you not use the trim to bring the bow down?

Yes I can bring the bow down but boat drags in water and slows way down, I am just trying to get max speed with 2 on boat without it porposing out of control.

[two stroke mick]

To be blunt think you are expecting too much from such a small boat. I also think that at the speeds you mention there is a high risk of chine walking. Those speeds on such a small boat may lead to serious injury or worse. Tsm

[HDAV]

Hmm can't picture it really once the boat is on the plane it should level our and if the nose is too high a little trim should bring it down? But without loosing too much speed we have 3.4m with 25hp 2 stroke and it will plane 2 up no issue but is centre console rigged and 2 up I do need to stand and lean over the wheel to level it out on the plane but once there it sits nicely, it will level out its self but takes a while even towing a doughnut with spotter she planes fine just needs a bit of help to get the nose down.

If your wife stands mid ships while you apply throttle then sits what's happens?

30hp 4 stroke off the back plus people at the rear on such a short hull.....

[beamishken]

If your wife stands mid ships while you apply throttle then sits what's happens?[/QUOTE]

She falls out the back probably lol

[lukewhiting]

I would change your prop for a stern lifting one. It should keep the bow down and more balanced