jackplate_or_notOPBack deckPalatka, FL29 posts, joined Nov 2025#1
Rig 2020 Bass Cat Puma FTD, Mercury 250 Pro XS
2020 Bass Cat Puma FTD, 250 Pro XS, Mercury Fury 4 blade 24 pitch, hydraulic jack plate with 6 inches of travel. boat runs fine but the guy i bought it from told me "run the plate all the way up, that is what it is for", and every time i do that at wide open the water pressure gauge drops from about 30 psi to under 15 and the motor sounds wrong.
i have read a hundred posts and they all say "watch your water pressure" and none of them say what the number should be. so the question is simple. what pressure is safe at cruise and at wide open on a Pro XS, how fast does it drop when you are too high, and is the 6 inch plate just not meant to go all the way up with this prop.
i fish the St. Johns, so a lot of runs are shallow and i want the motor up where i can.
merc_pro_xs_techTop tenClarksville, TN137 posts, joined Nov 2025#2
Rig 2015 Ranger Z518, Mercury 200 Pro XS
i work on these for a living at a dealer up near the Kentucky line, so here is the shop answer, and then go check the real numbers in your own operation manual, because they are in there.
water pressure on the 250 Pro XS is not one magic number. it climbs with rpm. at idle you may see almost nothing on the gauge and that is fine. what you are looking for is that it rises smoothly as you come up on plane and stays up at cruise. somewhere in the mid 20s and up at wide open is a healthy motor on most of the boats i see, and if it falls into the low teens and stays there while you are holding throttle, you are starving it. pull the plate down until it comes back.
the setup routine i give people: set the plate where the anti ventilation plate is about level with the bottom of the hull, run it at wide open, bring it up a half inch at a time on calm water. watch three things. rpm, speed on the GPS, water pressure. when the speed stops going up or the pressure starts falling, go back down a half inch. that is your number for that prop and that load.
the guy who told you all the way up was guessing. a 6 inch plate gives you room for shallow running at idle and slow speed, it is not a target. and the Mercury dealer locator and the manuals are all at mercurymarine.com, look up your serial and pull the actual spec sheet rather than trusting me or the guy at the ramp.
mod_curtis_hModeratorRussellville, AR212 posts, joined Nov 2025#3
Rig 2018 Phoenix 819 Pro, Mercury 250 Pro XS
my Phoenix 819 with a 250 Pro XS and a Tempest Plus 24 ends up around 2 1/2 inches up from the bottom of the plate with two of us and a full tank. three inches and the pressure starts wandering. it changes with a full livewell too, more than people think.
also check the pickup holes on the gearcase nose before you chase numbers. mine had dried mud wasp nest in one of them in march and i spent an afternoon blaming the plate.
sunday_draw_guyFront deckMany, LA74 posts, joined Nov 2025#4
Rig 2013 Skeeter FX20, Yamaha VMAX SHO 250
Yamaha side for whoever finds this later. the VMAX SHO 250 on my Skeeter FX20 is less fussy about height than the Mercs i have run, but it will blow out in a hard turn if you leave the plate up. learned that coming around the point at Pendleton bridge with my brother in the back seat. he still brings it up at Thanksgiving.
i run a Yamaha Saltwater Series II 25 pitch and the plate is about 3 inches up on mine.
jackplate_or_notOPBack deckPalatka, FL29 posts, joined Nov 2025#5
Rig 2020 Bass Cat Puma FTD, Mercury 250 Pro XS
did the half inch at a time thing this morning on Crescent Lake, flat calm, me plus a full tank, livewells empty.
plate at 1 inch: 5,800 rpm, 68.1 mph on the Garmin, 32 psi.
1.5 inches: 6,000, 69.4, 31.
2 inches: 6,050, 70.2, 30.
2.5 inches: 6,150, 70.0, 26 and wandering.
3 inches: 6,300, 69.0, 18 and falling, and that is the sound i was talking about.
so 2 inches is my number. four inches of plate i never use at speed. still nice to have at idle on the river.
merc_pro_xs_techTop tenClarksville, TN137 posts, joined Nov 2025#6
Rig 2015 Ranger Z518, Mercury 200 Pro XS
those are good clean numbers. note how the rpm kept going up past 2 inches while the speed went down. that is the prop starting to slip and ventilate, and a lot of guys only watch the tach and think more rpm means faster. it does not.
if you ever change props, do the whole half inch routine again. a 4 blade and a 3 blade want different heights on the same boat.
late_fall_smallmouthFront deckChattanooga, TN88 posts, joined Nov 2025#7
Rig 2019 Nitro Z21, Mercury 250 Pro XS
saving this thread. i have been running my Nitro with the plate pinned where the dealer left it in 2019. just did the routine on Chickamauga, i was a full inch low the whole time. picked up 1.5 mph and the bow does not plow on the long runs anymore.
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