Mayden Voyage

[Geff577]

Mayden vayage is done and dusted. What a stressful experience, thankfully everything worked and nothing was broken. So releaved when the boat was finally back on the trailer!

On the fishing front had a few bites but nothing big enough to take home.

Something odd was happening when driving the boat.
Not sure how to explain it water was calm and whilst crusing the front of the boat would suddenly start bouncing.
Google search of what was happening comes up with the term 'porposing'.

Boat is a haines signature 1750L with a suzuki 115hp 4 stroke motor.

[hornet]

Trim on the engine controls the boats attitude / angle on the water .. also weight distribution.

[Delirium]

Hi Geff,

+1 what Hornet said. It sounds like you may have too much weight forward....this allows for the centre of lift to get behind your CoG at higher hull speeds and sets up the porpoising cycle. Try getting some of your load aft of the centre of the boat. Radical engine trim settings can sometimes cause it on its own, but your case sounds like a CoG issue. A bit of trial and error should sort it out. Just make sure you have your engine trimmed in a fairly neutral range (roughly perpendicular to the waterline....or slightly 'out' from there) while you experiment with the load distribution. Keep in mind that if your fuel tank isn't located somewhere near the CoG of your boat, then your fuel load can vary your CoG.

Cheers, Ian.

[Nude up]

I would have thought the opposite would happen if you have too much weight fwd the boat would tend to bow steer and run slower than normal weight aft would give more bow lift it would be more susceptible to porpoising. Google trimming your boat there are many articles about it. I don't know what the Suzuki trim gauge units are but I have a Yamaha scaled at 1 to 5 with 5 being full bow down trim engine full in towards the transom.1 is full bow up trim engine full out. When I first hit the water I trim my engine to 3 units this seems to be the position my boat likes it's a Haines 650 classic if it is very calm I can trim the leg out to about 2 the revs will increase the bow will rise and speed will increase as less of the boat is in the water however if the boat hits a wake it can induce porpoising. When it is choppy in the bay I trim my leg in to about 4 or 4.5 this will keep the nose of the boat down and punch through the chop and stop the boat getting air note as you trim in the engine revs will reduce,speed reduces and if you trim in to far the bow will dig in and become unstable especially if you try to turn.
All boats like different trim settings next time you go out start half way and see what effects the trim has on your boat I would recommend google trimming your boat there are many good articles on the net.

[hornet]

My mate had a 4.9 markham whaler twin hull with twin 60hp engines that used to porpoise, he ended up fitting those plastic wings on the cavitation plates of the outboards to stop it...

[Delirium]

I would have thought the opposite would happen if you have too much weight fwd the boat would tend to bow steer and run slower than normal weight aft would give more bow lift it would be more susceptible to porpoising

Whether this boat is truly porpoising or not I certainly don't know (am only assuming it is based on the description). But if it is, porpoising is a dynamic cycle that is induced by the CoL moving aft of the CoG while planing. The CoL moves further back the faster the hull moves through the water and if it moves beyond the CoG the forward thrust exerts a downward force on the bow which increases drag and slows the hull. As the hull slows, the CoL moves forward again in front of the CoG, raising the bow, releasing the drag on the hull and allows the boat to accelerate again. As it accelerates the CoL starts moving back again until it again overtakes the CoG...completing the cycle and starting a new one.

That type of cyclic porpoising isn't a symptom of thrust angle.....it's a symptom of the CoL and the CoG trading places while under any thrust. It is almost the same phenomenon as a plane that 'rollercoasters' under certain conditions.

If a boat is slapping its bow up and down after being disturbed by a wake etc, then yes it is heavy aft and/or trimmed wrongly....but this will usually subside naturally as it causes it to lose some speed. You can also accelerate out of this type of situation, whereas true porpoising usually only happens in calm water where there is nothing to upset the cycle and it will keep on doing it until the power is reduced or radical trim applied. And the faster you go....the worse it gets.

[Geff577]

Lots to think about, I am not sure what was going on myself.

Boat was pretty empty, few rods and eski so not much weight to move around.

I will try adjusting the trim on the weekend.

[Texas]

I would have thought the opposite would happen if you have too much weight fwd the boat would tend to bow steer and run slower than normal weight aft would give more bow lift it would be more susceptible to porpoising

Whether this boat is truly porpoising or not I certainly don't know (am only assuming it is based on the description). But if it is, porpoising is a dynamic cycle that is induced by the CoL moving aft of the CoG while planing. The CoL moves further back the faster the hull moves through the water and if it moves beyond the CoG the forward thrust exerts a downward force on the bow which increases drag and slows the hull. As the hull slows, the CoL moves forward again in front of the CoG, raising the bow, releasing the drag on the hull and allows the boat to accelerate again. As it accelerates the CoL starts moving back again until it again overtakes the CoG...completing the cycle and starting a new one.

That type of cyclic porpoising isn't a symptom of thrust angle.....it's a symptom of the CoL and the CoG trading places while under any thrust. It is almost the same phenomenon as a plane that 'rollercoasters' under certain conditions.

If a boat is slapping its bow up and down after being disturbed by a wake etc, then yes it is heavy aft and/or trimmed wrongly....but this will usually subside naturally as it causes it to lose some speed. You can also accelerate out of this type of situation, whereas true porpoising usually only happens in calm water where there is nothing to upset the cycle and it will keep on doing it until the power is reduced or radical trim applied. And the faster you go....the worse it gets.

I'm definitely not buying a boat.
My CoG has moved to the waist line & I have enough trouble on dry land.

You're obviously not just a pretty face
Gra

[Geff577]

Second voyage on the weekend, front started bouncing at roughly 45km/hr in calm water.

Tilting the motor all the way down helped a little.

Boat was empty except for a few rods, safety gear, small eski 1 adult and 1 kid so not weight to move around.

I did have my son move forwards and backwards but it made little difference.

Upside my son his first fish and we managed to keep 5, 3 squid and 2 flathead.

[Lightningx]

Bet your son was happy to land his first fish.
Nice catch