Boat Performance Questions

[fenwick4life]

Hey Guys,

I have a few questions around the performance of my boat. Couple of years ago I went out and bought a 2005 Alumacraft Navigator Sport 18.5 with a Suzuki DF140. Since then I have been pretty frustrated with the boat's performance, mostly the top end. When I bought the boat it would top out at 32 with a 3x14x21 pitch prop. With that I could barely get out of the water and with three people I was plowing water the whole time. Max rpm was around 5200. Since then I have dropped down to a 3x14x19 which helped the hole shot and even my top end hitting 33. Then I went to a 3x14x17 to see what difference that would make, way better hole shot but top speed dropped to 30, which I expected. While running WOT the motor is fully trimmed out once on plane. I have checked the back foam for water log and so far so good. I will be checking the front after this weekend. A report was put out by Suzuki on a 2012 175 Trophy (which weights more than mine) with the same motor and it hit 45 mph. Needless to say I feel I should be getting more top end out of this motor.

So anybody have any advice on what to look for next or have a similar set up and let me know what your performance is? In addition, if I were to bring the boat in to have it looked at, anybody have any recommendations in the Bismarck area?

Thanks All,

 

[shorthairsrus]

They are not known for speed -- the hull design is from a lund engineer defected a long time ago. I raised my motor all the way to the top. I have to run 87 octane -- then I achieve my ideal Rpms Boat speed is around 44.

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that's on a good day and with a 150. You need to get your rpms up -- what is ideal for that 140?

 

[SDMF]

Where does the spray start when fully trimmed? Sounds to me like there's a good chance you've got significant hook in the hull.

 

[Allen]

I don't have an answer for you, but those are indeed some god-awful numbers, IMHO.

SDMF may be onto something with the hook comment, but I didn't think Alumacrafts were known for that problem, mostly Crestliners and other less expensive aluminum manufacturers.

This may sound stooped, but have you changed the sparkplugs? In my Yamaha, plugs are really important. Even when they look just fine, replacing them seems to put the horses back under the hood. Not sure I fully understand why it's so damn sensitive to plugs, but it really is...

FWIW, I would have guessed you'd be pushing the upper 30s fully loaded and lower 40s when running light.

 

[fenwick4life]

Well sounds like I have one thing to take a look at. To be honest I have never heard of a hook in the hull before. Quick google search and I am picking up what you're throwing down. I'll check it out after work. Last I checked the plugs were good but thanks for the thought.

Appreciate the input so far.

 

[Ericb]

Im assuming you boat the boat used since 05 is more than a few years ago. In that case you think the previous owner had it proped right with 21p. I know its a big assumption. Id also like to think the moter hight would be correct. You may want to double check this, there was a good post on here abiut it a few months ago. Have you had a mechanic look at your engine? Did you check compresion when you bought the boat?

Ive had good luck taking my boat to Toy box in Mandan.

 

[Zogman]

Call Ricky aka Prop Man on Walleye Central. Give him all the details he will ask a few questions and have some good suggestions.

www.BrainerdProps.com

218-824-0000 Ricky Besmehn

 

[Captain Ahab]

That motor should be hitting over 6000rpm on top end. Sounds like you have tried props so I would look at engine height. If that doesn't work, it's likely low output from engine. I did read about some efi four strokes getting clogged or gummed up injectors in the past.

 

[shorthairsrus]

WOT should be 6k ---- start with the engine. How fresh is the fuel in it? Hopefully no ethonal and you have it treated.

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fresh 87 octane vs. 91 makes a difference of 100-150rpm on my motor. Not only does it like the fuel unstable it likes it fresh and I always use a conditioner.

 

[SDMF]

On flat water, if you're seeing spray past the side of the hull any more than ~2' ahead of the transom then you're plowing. Hook, engine height, or both.

The 140 Suzi isn't their "strongest" offering, it's the most HP available on the block they also use for 90/115. Wild-assed guess, if you get that combo to 38-40MPH, that's probably about what you're gonna get.

 

[Vollmers]

With your eyes, fingers, & toes crossed!

On flat water, if you're seeing spray past the side of the hull any more than ~2' ahead of the transom then you're plowing. Hook, engine height, or both.

The 140 Suzi isn't their "strongest" offering, it's the most HP available on the block they also use for 90/115. Wild-assed guess, if you get that combo to 38-40MPH, that's probably about what you're gonna get.

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I run an older trophy 190 w/175 two stroke. With just me in the boat & a slight chop the best i've ever gotten was 45.3 (GPS). Your boat is only 1/2 shorter with 35 less HP plus the 2/4 stroke factor. I'd be tickled 3 shades of pink to get 38-40 out of your set up like SDMF mentioned above. Alumacrafts are good boats but not SPEED DEMONS by any means. What is your boat max rated for? I would imagine 175 maybe?

 

[SDMF]

I should've asked what your prop looks like too. Pristine vs. chewed can easily cost you 2-3MPH and if chunks are missing lots more than that.

 

[KDM]

My trophy 185 with a 135 mariner 2 stroke can get me to about 40 depending on loadout and water conditions. The boat is rated for a 175, so I'm leaving lots on the table with a 135. Not a speed freak, but it gets me where I want to go and I can read the water with enough time to avoid obstacles.

 

[Riggen&Jiggen]

I have a Viper 180 and it has a 140 Johnson which is a Suzuki. I have 21 pitch 3 blade stainless and I get 41 mph by myself and no trolling motor batteries. Live well full, full gear, 2 trolling motor batteries and 2 guys I get 38 mph at 6K rpm. I am sure my glass boat weighs more than your acraft. Key thing is rpms. If you are getting 5.7 to 6K top rpms with a 21 pitch prop and you can only get low 30s for speed I would say the motor needs to be raised our something is wrong with they hull of the boat.

 

[SDMF]

Assuming hook, getting the hook outta the hull will GREATLY improve ride quality as well as the hull will no longer be mechanically slapping you down onto the next wave. The boat will get 2x-3x drier as well if hook is the problem and you resolve that issue. My '06 Crestliner FishHawk had terrible hook from the factory. 41-42MPH w/150Suzi on day one w/23 pitch prop, rough and wet. Fiddled with 5 props and 4 motor heights before taking it back to the factory to be dehookified.

 

[Rowdie]

What's it mean for the to be 'hooked'

 

[SDMF]

What's it mean for the to be 'hooked'

Slightly concave on the hull side where the hull and transom meet. Helps the boat plane @ lower speed buy forcing the nose down, faster you go the downer the nose gets forced, keeps the keel of an AL boat planted to minimize "sliding", helps the hull track a little better on plane, and of course the biggie, allows for faster planing with less than max HP, as example, allowing 115HP motors to perform at least satisfactorily on hulls designed for a 150.

 

[Sub_Elect]

I would bet anything your motors too low. Have someone run it wide open and trimmed out and check the cavitation plate. It should be just above the water. If it's under the water than its too low and needs to be raised. I would almost bet money it's your problem.

 

[SDMF]

I would bet anything your motors too low. Have someone run it wide open and trimmed out and check the cavitation plate. It should be just above the water. If it's under the water than its too low and needs to be raised. I would almost bet money it's your problem.

I'm bettin' hook. Seen an awful lot of Alumacrafts throwing spray well ahead of the windshield on piss flat calm water.

 

[deleted member]

So how do you fix this hook thing?