22 dlx 90 hp mercury 4stroke

[62larkowner]

recently purchased a 2013 suntracker 22 dlx fishin barge, ( 2 logs) with a 2013 mercury 90 hp fourstroke, factory prop 13.8 x 13p 4blade, WOT range is 5500- 6000, started out at about 5800 rpm wot and 16 mph adjusted motor up 2 holes to get cavitation plate closer to bottom of hull,
my current wot is at 6200 rpms and about 19 mph, from research ive learned this set up should hit mid to high 20s
adjusting trim seems to show no difference and load hasnt made much difference.

need advice to figure out issue

 

[HotTommy]

Visit the Mercury Prop Selector website and input your data to see if a different prop might help. https://www.mercurymarine.com/en/ca/propellers/selector/

 

[ahicks]

When it comes to speed, your 4 bladed prop may not be helping a thing. They're way more about hole shot and low speed maneuvering. On a conventional hull, something capable of 30mph and higher, I would think the 4 blade would be a step backwards for those where top speed is a priority. On a pontoon boat, because of the lower speeds in play, not sure how critical that is.

Mid to high 20's may be a bit optimistic in my experience. High teens to low 20's would be closer, and that's going to depend on your load/how much junk you're carrying around under the seats/number of coolers in use.

In the .pdf I've attached, is an article with a pontoon speed chart about half way down. It's been around just about forever. I've seen it to be scary accurate to date, supplying data to give you a realistic idea of what to expect with power and length combined.

 

[62larkowner]

Visit the Mercury Prop Selector website and input your data to see if a different prop might help. https://www.mercurymarine.com/en/ca/propellers/selector/

i had actually tried that first but when it got to current WOT (6200) the lowest speed it showed was 25 and mine was only 19 mph

 

[HotTommy]

Top speed for a boat is determined by the maximum power output of the engine (usually at WOT), the total drag on the boat (water and wind), and the efficiency of the propeller in converting the power of the engine into thrust to propel the boat. If the propeller has too little bite on the water, the engine RPM may go above the recommended maximum. If the propeller has too much bite it may cause the engine to hang up at an RPM well below the recommended maximum. But in some cases, the propeller's bite will slip more and more so the RPM can rise without causing the boat to go faster. The difference between the ideal speed of the boat with a 100% efficient propeller and the actual speed is the slippage. The target slippage for most boats is 5-20%. The calculated slippage for your boat is 42%.

I suspect a less aggressive propeller pitch would improve your slippage and may increase your speed slightly. Even with the optimum propeller I would be surprised if you gained more than 1-2 MPH.

 

[ahicks]

i had actually tried that first but when it got to current WOT (6200) the lowest speed it showed was 25 and mine was only 19 mph

There's one other thing in play, or perhaps a different way of showing what Tommy is talking about. My 24' boat w/90 Honda will turn up about 6200 using a 13" pitch prop (3 blade) and run in the low 20's. Tons of acceleration on tap for pulling tubers. When I went to a 15" prop, rpms dropped to a much more civilized 5500rpm and my speed increased a couple miles an hour to 25-26mph. Still plenty of punch, but not near what's available with the 13p.

I've set up a bunch of boats using 40-90 hp Honda's (they're all I work on) and have learned that they do much better at 5500 than they do at 6k. FWIW

 

[legalfee]

I think you'd be better off with a Quicksilver 3 blade 13 pitch.
I'd also check your pontoons for water.

 

[Starcraft5834]

ive got a Starcraft EX-R 20 with 115 merc... 3 blade 15p. will do 30 lightly loaded. would think 22 w 90, you'll be bout 20.. ish give or take a few mph.. only floored my set up once to see what it will do.... dont plan on doing it much.... if i wanted speed would have got a V hull.

 

[EngineNoO9]

I have a 2001 24’ aqua patio pontoon with the carb’d Mercury 90 hp 4 stroke but it has a 3 blade prop (black max 14” diameter 13 pitch) and it’ll do 26 mph with a couple people. Fully loaded it’ll still push about 23mph (could probably do better if I tell some people to move further back). It’s either your prop or just the limitations of your hull.