small motor - big boat

[water proof wick]

I have a 19 ft 1500 lb boat , 7.8 ft beam 200lbs of fishing gear, me and two fat friends with a 1995 88spl Johnson . As of now the boat will plain without struggling and has a max rpm around 5300 -5400 rpm , I can back of to about 4700 rpm at 18 /19 mph and it will still plain but the boats wants to be at 5000 around 23 mph . The prop is a 14 x 17 three blade that came with the motor stock ( I think ) I would like to get it to plain of at lower rpms and still maintain a 5400 rpms , is this possible

 

[H20Rat]

Move more weight forward &/or add smarttabs. Changes in prop aren't going to get you were you want to be.

 

[bajaman123]

what is the max recommended RPM of the engine? I am inferring from your post that you want to be able to stay on plane (not plain) at a lower rpm? Have you considered switching to a 4 blade? If not, I'd consider it, in the same 17" pitch.
What diameter of prop do you currently have, by the way? What brand, too, if you know?

 

[82rude]

I switched to a solas amita 4 blade prop for my boat and motor and am 100 percent happy with the results.I can stay on plane at lower rpms,cruise at lower rpms and it comes out of the hole good with almost zero loss of top end.Amazingly enough it was originally for a 17 foot woody with a 90 evinrude ,but it has translated excellently to a 60 e-tec on a 16 foot starcraft bowrider.I have 15p s/s,2 17p aluminums ,one cupped and one not and the 17p solas.All around performance is so much more superior with the solas.Try one, I think you will be pleased.

 

[ttankmoran]

Something isn't right, 5000 RPM and only 23 MPH? thats about 42% slip! and about 50% at 4700 RPM

Can the RPM and speed be verified? I'd be looking into a spun prob hub or a prop that has been re-pitch, where did the engine come from? off a pontoon?

That is a big boat, but if its only 1500 lbs I would think you should still be able to get into the 30-35 range with that engine.

 

[water proof wick]

I will be working on the boat tomorrow , I will take some pics of the prop and get all the details I can . The numbers on the prop are 14 x 17 176214 d3 . It is the original engine and prop for the boat . The prop and lower unit appear to be in good condition with no dents . I measured the diameter an came up with 12.5 maybe a little less . Full throttle range as per manual is 4500-5500 and max hp is 5000 rpm . the engine does not struggle a bit . revs out fast , to fast . I removed the prop it all seems good as far as the condition of the spline . I really appreciate the interest in my post thankyou

 

[water proof wick]

I bought the bought from an old couple that never drove the boat . I don't think it ever left the river with a 10 mph speed limit ,it has maybe 100 hrs total . I am sure it was never prop tested for lake cruising speeds for those wondering, they bought it and it just sat at the dock all summer year after year with the exception to use it to go for dinner a mile down the river , so this would be the first time its ever had a prop change

 

[water proof wick]

smart tabs ?

 

[82rude]

I had a 1990 lb. glass boat with a 1982 90 rude and could eek out 33 mph with a 14x17p prop at around 5500 or so (not positive anymore).so your prop maybe spun and slipping.look up nauticus smart tabs on the web.http://www.nauticusinc.com/ they do work great but will not cure a pooched prop.you can test a rubber hub prop by marking a line on the rubber and also the hub and if after testing they have moved your prop is spun.

 

[steelespike]

You need to do a lightly loaded wot rpm and gps speed.I feel that your tach is not accurate.
Calculates at 42% slip Normal runabout slip would be about 12% at wot.The tach is all;ways suspect when numbers are whacky.

 

[water proof wick]

ok I have a gps , im going to remove the prop mark it , the prop looks perfect still has all the paint no dings or dents . I am not sure how to check rpm other than hook a second tach up. I have only owned two boats this alumacraft trophy 19 and a sea nymph 191 CC with a 75 merc and the sea nymph was much faster and planed easily at low speeds but i can tell by towing the two the alumacraft is heavier. If all goes as planned today i should have mph numbers by the end of the day . my goal is just to get the boat to plane without having the motor spinning at 5000 , i really don't care how fast the boat goes it just feels like the boat is pushing way to much water unless i put the hammer down , maybe i am just use to the sea nymph poping up and gliding across the lake with little to no effort

 

[Sea Rider]

If you have a heavy boat forget all about getting out of the hole with less rpm, need way more rpm to get out of the hole faster specially if loaded. If engine runs inside its factory wot range not an issue, best would be running near the max, you can always throttle less to maintain plane speed with less rpm if hearing those high rpm is what bothers you.

Describe " it just feels like the boat is pushing way to much water unless i put the hammer down" do you have back water splashes of some sort ?

Happy Boating

 

[inthedirtagain]

I had a 12.5X17p on my Merc 1000 that was hard to maintain a good plane while moving slowly. There just isn't a lot of surface area for that small of a prop to grab. At WOT, it would push my 16ft Silverline to about 38mph with just me in it. Holeshot stunk, pulling kids on skis or tube stunk......just not enough "grunt." Switched to a 4-blade today and its a night and day difference.

 

[water proof wick]

so had the boat out today me 260 lbs friend 250 lbs , , 20 gallons of fuel , I got 28.9 on gps at 5400 that was wide open at the end of the day in perfect chop I got 30.2 on gps and it was running 5600 rpm . anything under 4700 the boat starts pushing a lot of water and the motor starts working hard , it wants to be at 5000 rpm . so im thinking that is all she is going to give me considering the weight vs power . not sure if a better prop would help so im not wide open all the time ,, any thoughts ?