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 Post subject: Boat top speed questions
PostPosted: 22 Mar 2017, 20:28 
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Joined: 08 Feb 2017, 09:20
Posts: 59
First off, I know I don't have a tach. It's been years since I ran an outboard.

My setup is a 17' aluminum bass boat, with a jack plate 6" set back, and an Evinrude 70 2stroke. Manual tilt

It rockets up to full speed, but it's about 36mph. Will let me back off and cruise 32or so easy.

Does that sound about where it should be? I just feel like it should be quicker. Maybe mess with the prop? Tilt more? Raise jack plate more? Any tips feel free.Image

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 Post subject: Boat top speed questions
PostPosted: 22 Mar 2017, 22:51 
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Joined: 12 Dec 2014, 14:32
Posts: 2069
Location: Eastern Mass
I get to 40mph in a 16', 16-degree deadrise V-hull, heavy (hull only ~710-pounds 'dry') with just an Evinrude 60hp on the stern. And I'm intentionally propped 1" low on the prop pitch (to carry more loading).

So I'd say you really need a tach for that rig, even one of the 'Tiny Tachs' for $30 - $40 you just wire to a plug wire. You probably have a lot of hull in contact with the water, being a flat bottom hull and that robs you of efficiency.

I would think that you should be zooming soooooooooooooooo fast as to almost require a change of clothes .. :shock: !



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 Post subject: Boat top speed questions
PostPosted: 23 Mar 2017, 08:30 

Joined: 24 Mar 2015, 19:18
Posts: 209
Location: Florida
Yep, any guess is a shot in the dark till you get WOT RPM numbers.



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 Post subject: Boat top speed questions
PostPosted: 23 Mar 2017, 16:07 

Joined: 17 Aug 2016, 20:52
Posts: 350
Location: NJ
Much to consider when talking top end, one persons hull might just be a slow hull, go to any makers web site and look at performance bulletins, you'd be surprised to see 2, 14' hulls with the same engine have a 5 MPH difference. In the case of your engine, how well is she tuned, the prop, what shape is she in? Is your hull clean and smooth?


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 Post subject: Boat top speed questions
PostPosted: 23 Mar 2017, 17:53 

Joined: 28 Jul 2013, 19:04
Posts: 70
Fin on the Motor should be on the same plane as the Boat bottom. Put motor in the operating position, put a Straight Edge on the Boat Bottom. Adjust the Jack plate to match. Try tilting the Motor to different positions. Use a GPS on a Smartphone for MPH. GOOD LUCK!


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PostPosted: 23 Mar 2017, 18:31 
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Joined: 08 Feb 2017, 09:20
Posts: 59
I have fin slightly above boat bottom. Will adjust trim this weekend and play with Jack plate again.

Motor is running like a champ, great compression, smooth idle. Prop has a few dings though that may rob some, but no vibration. This boat ran mid-high 20 with a 35 short shaft.

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 Post subject: Boat top speed questions
PostPosted: 25 Mar 2017, 16:32 

Joined: 05 Oct 2008, 12:14
Posts: 4143
Location: Algonquin Il
With 6" of set back you should be able to raise the motor about 1.5 inches above the bottom of the hull.



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PostPosted: 26 Mar 2017, 13:56 
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Joined: 08 Feb 2017, 09:20
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lckstckn2smknbrls wrote:
With 6" of set back you should be able to raise the motor about 1.5 inches above the bottom of the hull.

Ok, so motor is now raised up ended up like you said 1.5" before it was too high.

Got it trimmed up as much as possible without porpousing. 36mph with me and kid and gear. 34 with me, kid, and another 250+adult. Think I need more of a speed prop. I'll see what numbers are on the prop and post up later.

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 Post subject: Boat top speed questions
PostPosted: 26 Mar 2017, 14:06 

Joined: 05 Oct 2008, 12:14
Posts: 4143
Location: Algonquin Il
You will need a tach to find out which prop is best.



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PostPosted: 26 Mar 2017, 14:42 
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Joined: 08 Feb 2017, 09:20
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Will any cheap tack work? I think I just hook into the grey wire in my controls?

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PostPosted: 27 Mar 2017, 10:56 
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Joined: 08 Feb 2017, 09:20
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Image

I think one of these would get the job done. I'm curious if I really need to run it all the way to a spark wire, or if I can plug it into my controls where the tach wire is?

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 Post subject: Boat top speed questions
PostPosted: 27 Mar 2017, 17:04 

Joined: 05 Oct 2008, 12:14
Posts: 4143
Location: Algonquin Il
That style of tach reads the firing of the spark plug.



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PostPosted: 27 Mar 2017, 17:22 
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Joined: 08 Feb 2017, 09:20
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lckstckn2smknbrls wrote:
That style of tach reads the firing of the spark plug.

So I'd need to leave it back there and have someone look at it while running? This is so complicated. I can't believe it's this hard to get the right prop. For our inboards you can tell them what boat and motor you have and they'll tell you exactly what prop will do what performance, rpm, full speed, torque, etc.

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PostPosted: 30 Mar 2017, 17:14 
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Joined: 14 Sep 2016, 14:53
Posts: 87
Just add some wire

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PostPosted: 31 Mar 2017, 22:57 
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Joined: 08 Feb 2017, 09:20
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WALI4VR wrote:
Just add some wire

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Alright. Got the tach ordered. Going out tomorrow. Will play with the jack plate a bit more. Also going to run some seafoam and change the spark plugs.

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