Misbeheaving HST ...

[dompie99]

Good day to all,

I finally had my rig out to the water yesterday and after a few hours of low to mid rpm run, i decided to push it further.

When I reach about 80 to 85 mph, this babe start to chinewalk like if I was on a V-Hull...WTH ???

I tried different trim and height settings but it seems that there is womething that was not there last year !!

Hydraulic jack plate ( land and sea ), Setback ot 10'' on top of the jack plate ( total of 14'' )

Solid mounts, 3.0L V6 225hp Merc and some mods to it ( carbed )

May be soneone can help me pinpoint the prob.

[dompie99]

bump

[David - WI]

Grab the lower unit and yank it around... could be a broken or loose bolt or motor mount or maybe the transom is shot. If you have 10" setback plus a 3-liter hanging off the jackplate; maybe the plate is worn out or broken?

[rankink]

Other than what is mentioned above how heavy is that 3.0 engine? Seems like many with the heavier (non 2.5) engines less setback is needed on these boats.

[panther150]

14" setback is too much for a 3 litre motor hopefully you have the setback in front of the jack plate as the land and sea are not the strongest.Post pics of your motor/ jack plate. what is your prop shaft height? with 14" setback should be even to 1.5 " plus above the pad. sounds like you have a broken motor mount or some issue with your steering without any more information to go on. Check your steering for play and motor mounts. I would not run more than 10" with that motor. I run 14" on my AE-21 with a 2.6 Yamaha witch weighs roughly what a 2.5 Merc does with great results. I run about 1.5" above the pad for max speed with one aboard. What prop are you running?

[dompie99]

Thanks for the input, Indeed, the jackplate is before the land and sea jackplate, the height is between even to the bottom to about 1.5'' above, the steering is an Hydraulic Seastar with the helm from the same manufacturer, and the prop is a 32'' cleaver.

I will post pictures in the next few hours

[dompie99]

Here is the picture promissed, as you could see, the items are has stated.

[BarryStrawn]

I don't know much about the HST but that looks extremely low which will cause all kinds of handling issue. I'd guess you need to turn the Slidemaster jackplate right side up to get to a better height.

[whipper]

my guess is the cleaver is creating so much lift your running on the centre pad very lightly and the out side sponsoons are air board. that would be like driving a vee hull hence the chine walk. Just a guess. Before i read you were at 1.5 above i would have thought maybe your to low. If your low with lots of lift you could essentially run on the gear case with the torque of a 3.0lt and a 32 cleaver. So thinking about it some more since you have 14 inchs of setback you might even be able to run higher to get the stern planted more at speed? its alot trickier than most think to measure were your at to the pad. Level ground level trailer level everything!! haha A garage isnt even level they usually slop to the out side an inch or so. Your describing a motor with torque running at speed to low with a big good lifting wheel. If the wheel is larger dia you can run higher than one that has a smaller dia as an example. Hmmm Those are my thoughts. i would try a 30 drag4 and triple check the gear case height with a level on the flywheel so you know your at neutral trim.

[speedinstream]

At speed it is a pad vee the sponsons are there to keep it from going to far like training wheels you will still have to drive it no matter the setup

[David - WI]

The motor on my HST is not even 1" above the pad; and my tilt pin is about here:

[BarryStrawn]

the height is between even to the bottom to about 1.5'' above

Are you measuring height of the propshaft or cavitation plate? Because the position of the engine in your picture suggests the cavitation plate. So you would need to go up six or seven inches. The Slidemaster as rigged is lowering your engine.

[racer]

Steering ram is early seastar and the bushing in the center may be worm out. Do you have a pro version helm? Too much set back and wrong prop. What lower unit?

[panther150]

take a pic of the lower unit from the side with the motor at full lift showing both the lower unit and the bottom of your hull.I think Barry has a point with your setup and your plate is mounted wrong causing your motor to be way too low.As stated that is not a great prop for your combination. Mazco re4, re3, omc srx and mercury lightining ET are all good props for that hull. Some have had good success with Hoss props as well. This hull is not a pad vee as the hydrostream XT hulls where but a trimaran tunnel and should handle like a dream at 85mph if setup correctly and free of loose steering etc. Al ( Racer) above is VERY knowledgeable and has pointed out a potential problem with your steering, I would also check that out. While you are taking pics, post pics of the whole boat, always nice to see an HST.

[at100plus]

14" isn't too much setback as long as it's the proper setback and everything is tight with solid upper and lower motor mounts. The center line of the lower unit bullet should be about even with the pad or up to an inch above if water psi will allow on HST not much less. The lower the engine is the worse it will handle especially when letting off the throttle from 80+

HST should not handle bad at even 100 mph so something is very wrong. Did you bleed your steering this year and is do you have Sea Star Pro? I actually had an HST with no Pro Sea Star and did not have solid mounts with a 96 225 Vindicator and it handled rock solid an 88 mph.