Low speed

[procraftguy]

Ok 1998 Mariner 115 elpto 2 stroke 4800 max rpm 17 pitch alluminum 3 blade Michigan wheel prop 1998 smoker craft 2100 deck boat getting 23 .2 mph at 4750 rpm wot prop seloctor app only goes down to 28 mph for current setup when putting in info to get new prop any suggestions I have trimmed it and motor set up is good shop says everything is fine good compression and leak down test so any suggestions would help

 

[dingbat]

Ok 1998 Mariner 115 elpto 2 stroke 4800 max rpm 17 pitch alluminum 3 blade Michigan wheel prop 1998 smoker craft 2100 deck boat getting 23 .2 mph at 4750 rpm wot prop seloctor app only goes down to 28 mph for current setup when putting in info to get new prop any suggestions I have trimmed it and motor set up is good shop says everything is fine good compression and leak down test so any suggestions would help

Not familiar with your motor but your WOT seems rather low for an outboard. My outboard is propped at 5600 rpm

 

[procraftguy]

Max rpm on my tag says 4800 so rpms are in range

 

[dingbat]

Max rpm on my tag says 4800 so rpms are in range

What tag are you talking about? Everything I’m seeing say 5250

 

[ahicks]

So if it's turning 4800, the engine is making power. The reason for the low speed lies somewhere else. Like a prop that's in pretty bad condition, a really heavy water logged boat, or a hull covered with something (slime, barnacles, you get the idea).

For comparison purposes, my latest project boat is a '93 22' alum. Lowe deck boat w/120 Johnson. It's running 35mph easily, going into the wind with the top flopping around madly, at about 5000 rpm.

Point being, thinking you have something way wrong. It shouldn't take much to figure out what that is.

 

[procraftguy]

The serial # tag on transom bracket ... Mercury has there's listed as 4750 to 5250 but that doesn't match the info I have on motor and even at 5250 I feel that only a couple mph and I'm much slower then I feel I should be

 

[procraftguy]

Prop seems ok bottom is good it is fiberglass ways about 2900 lb light load hole shot is not a beast but fine I have owned many boats and usually no issues but this has me stumped

 

[Scott Danforth]

your at the bottom of the RPM range
weigh your boat, I bet your heavy

 

[dingbat]

The serial # tag on transom bracket ... Mercury has there's listed as 4750 to 5250 but that doesn't match the info I have on motor and even at 5250 I feel that only a couple mph and I'm much slower then I feel I should be

By the math you should be @ 37 mph if everything is setup right.
Is this boat new to you? Tachometer verified?

Pretty far off for there to be a problem with the prop that isn’t physically noticeable

 

[procraftguy]

Yes I bought it at the end of August last year had it in shop 2 times in the 60 day warranty from marina they said nothing is wrong as if I was just going to except it I haven't checked hub as I'm currently waiting on new trailer I have on order but from my experience with bad hubs there either good or bad and very obvious

 

[Starcraft5834]

Agree with Scott.......... there's what your WOT "should be" and what you are getting with your current prop... would suggest your over propped due to becoming heavy...I had a heavy cuddy when I bought it had to much prop, or pitch, would not get out of water.. put a 4 blade on it with less pitch.. it matched what I needed for boat weight, and motor... jumped out of the water fast.

 

[WesNewell]

Smoker craft makes a lot of models. For best results, provide a link to your model.

http://boatspecs.iboats.com/Smoker-Craft_Boats/bp/20br1444

 

[procraftguy]

http://boatspecs.iboats.com/Smoker-Craft_Boats__21_Sunship__1998/bp/66b83297. There's the link if it helps I'm going to investigate the foam and under deck too see if there's water in there it was sitting with a bent trailer for a long time tilted forward so it was full of water when I jaked it up so it was tipped back never thought of that thanks for the suggestion I am also thinking 4 blade prop

 

[ahicks]

If it's been stored nose down full of water, there's not a lot of doubt in my mind you have a water logged boat. It's very likely WAY heavier than it' supposed to be.

 

[dingbat]

Theoretical Speed in MPH = Pitch x RPM / Gear Ratio x 1056

17 x 4800 / 2.04 x 1056
81,500 / 2154.24
37.8 MPH

Percentage Slip - Actual speed / Theo speed
38.8 - 23.2 / 38.8
15.6 / 38.8 = 0.402
40.2% Prop Slip

Am I the only person that finds it a bit hard to believe that a properly setup motor, running a prop in "supposedly good" condition, is returning 40.2% slip?

 

[procraftguy]

Dingbat this is why I'm on here I have no clue why I'm running so slow heavy boat is best reason I have heard and the marina confirmed my work results and just said that's how those boats are I'm not convinced

 

[jimmbo]

Deck Boat as in a conventional hull, or as a Pontoon Boat?

 

[procraftguy]

it's a fiberglass trihull with pontoon rails and furniture

 

[Scott Danforth]

http://boatspecs.iboats.com/Smoker-Craft_Boats__21_Sunship__1998/bp/66b83297. There's the link if it helps I'm going to investigate the foam and under deck too see if there's water in there it was sitting with a bent trailer for a long time tilted forward so it was full of water when I jaked it up so it was tipped back never thought of that thanks for the suggestion I am also thinking 4 blade prop

weigh your boat and trailer. compare it to the spec

 

[Faztbullet]

Check the gear ratio as may have a 3 cylinder unit on it