H56 Set Up Question

[MDean89]

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[Arkyarcher]

It (or an even a longer one) should help get rid of it.

[MDean89]

It (or an even a longer one) should help get rid of it.

My goodness, time to sell it. Thank you!

[Arkyarcher]

Need more info, prop to pad, prop worked on, full trottle being achieved and whether it is a new problem or just started.

[Les Young]

Would a 6" manual jack plate contribute to my porpoising problem as well as my lack of rpms and speed? 2003 18' H56 with 2003 135 Opti., 4 blade S.S. 19P prop.

I had a 98 h-56 with aq 135 Mariner that had a 4 blade on it( can't remember exactly which one now) that wouldn't lift & was was slow as crap. I put a Vance 6" plate on it & an old Turbo 3 blade on it that gave it a lot of lift & i can't remember what pitch it was now, but would do 58 with 2 pretty heavily loaded & 60 with just me. Would have got more if i'd messed with the setup any. Wish i had it back now too.

[thebentpole]

No, the jackplate should help, especially rpms, but it may not be at the right height. What kind of rpms are you getting? 19P doesn't seem like it should be too much prop, On the JP, I'd start at 4" ptp and go up from there until you max rpms. Porpoising may just be too much trim...

[MDean89]

No, the jackplate should help, especially rpms, but it may not be at the right height. What kind of rpms are you getting? 19P doesn't seem like it should be too much prop, On the JP, I'd start at 4" ptp and go up from there until you max rpms. Porpoising may just be too much trim...

Only getting 4900 - 5000 rpms. Right now my jp is at its lowest setting, I’m not sure what my ptp is, I’ve never measured it and not too sure how to.

[MDean89]

Got boat to shop this morning. Tech. is telling me it's my ob set too high on the jack plate (which cannot be lowered anymore, bottomed out). He suggested removing the jack plate completely and swapping to a 3 bladed 21 - 23P prop.

[thebentpole]

Level your boat at the top rail using your trailer jack. Then level the centerline of your gearcase using trim & tilt. Measure from the pad to the floor and the gearcase centerline to the floor. Subtract pad to floor from centerline to floor and thats your prop-to-pad (ptp). I'd be leary of the advise your getting. I ran an 1998 H56 for 20yrs with a 6" jackplate ( Yamaha C115) and it was perfect. Would run 51 in its prime.

[Les Young]

Got boat to shop this morning. Tech. is telling me it's my ob set too high on the jack plate (which cannot be lowered anymore, bottomed out). He suggested removing the jack plate completely and swapping to a 3 bladed 21 - 23P prop.

Find a new mechanic.

[MDean89]

Find a new mechanic.

Ok, what are your thoughts? Some agree, you disagree.

[thebentpole]

Figure out your ptp and re-mount the motor on the jackplate so you can get 4" ptp +/- 1". That will allow you room to make adjustments with the jackplate. You may also want a different prop with the jackplate. The jackplate is not the problem.

[MDean89]

Finally got to measure, my ptp is exactly 5”. I only have room to raise my ob if I keep the jack plate. I can’t lower the ob anymore than what it is right now on the jp.

[Arkyarcher]

PTP set at 4" and see if it gets more RPM at wot, might have to adjust up but it should help top end and porpoising. May have to go to a 21 pitch prop if RPMs are too high.

[MDean89]

PTP set at 4" and see if it gets more RPM at wot, might have to adjust up but it should help top end and porpoising. May have to go to a 21 pitch prop if RPMs are too high.

Will do. Thank you!

[MDean89]

PTP set at 4" and see if it gets more RPM at wot, might have to adjust up but it should help top end and porpoising. May have to go to a 21 pitch prop if RPMs are too high.

Raised ob to 4” ptp. Rpms still at 4950-5000 and wot is 42 gps still. Still porpoising but ride seems “smoother”. Still have the 19 pitch 4 blade prop.

[Arkyarcher]

Raise it up a 1/4 inch at a time until your water pressure drops, then drop back down. See if your RPM at WOT increases. Weird that RPM's didn't increase some.

[snoopy]

are you getting wot? as in checking on engine not just hot foot floored

[MDean89]

are you getting wot? as in checking on engine not just hot foot floored

what is the best way to check it?

[MDean89]

Update, after researching and advice I went to a 4 blade 17p Mercury Spitfire prop. My rpms are up high enough now to hit the rpm limiter (5600) BUT my speed has dropped down to 38 mph. My ptp is at 4”. Did I go the wrong way with the prop or can I make a jackplate adjustment to lower rpms and get speed back?