1986 Frontier 25 Twin 150-HP

Optimizing the performance of Boston Whaler boats
quickenberger
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Joined: Sun Feb 05, 2017 8:48 pm

1986 Frontier 25 Twin 150-HP

Postby quickenberger » Fri Jul 17, 2020 3:01 pm

On a 1986 FRONTIER 25 there are twin Evinrude E-TEC 150-HP engines.

At 4,100-RPM engine speed the boat speed is 34-MPH.

At full throttle the engines accelerate to 5,400-RPM and the boat speed is 48-MPH.

The propellers have 17-pitch.

I don't have enough time yet for data on fuel burn at cruise. The boat has logged about 64-miles.

The route was depart Homer, pass Seldovia, on to Tutka Bay, and back to Homer.

ASIDE: I had a problem with one vapor separating tank at the fitting where the cooling [water] tube enters the [VST] housing. The O-ring seals are important to maintain. If they leak the VST will pull [in] air and water [to mix with the fuel]. [If that occurs after] the engine stalls under load, to restart will be hard.

jimh
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Re: 1986 Frontier 25 Twin 150-HP

Postby jimh » Fri Jul 17, 2020 4:27 pm

That you get 48-MPH with 17-pitch propellers is quite amazing at the engine speed of only 5,400-RPM.

quickenberger
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Joined: Sun Feb 05, 2017 8:48 pm

Re: 1986 Frontier 25 Twin 150-HP

Postby quickenberger » Fri Jul 17, 2020 5:33 pm

Boat speed over ground was 34.4-MPH at 4,100-Rpm

[Deleted image of tachometers and GPS receiver. Your word is your bond, no pictures necessary—Moderator]

jimh
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Re: 1986 Frontier 25 Twin 150-HP

Postby jimh » Sun Jul 19, 2020 9:36 am

My amazement was over the boat speed of 48-MPH at 5,400-RPM.

Assuming the gear ratio of the engines is 1.85, a 17-pitch propeller at 5,400-RPM engine speed cannot reach 48-MPH. The engine speed or the boat speed have to be wrong. Perhaps there was a strong current assisting the boat or the tachometers are off.

My engine has the same gear ratio and a 17-pitch propeller. At 5,700-RPM the boat speed will only be about 42 to 43-MPH. There is no way the boat could be driven by a 17-pitch propeller to 48-MPH with the engine turning only 5,400-RPM.

If the modern E-TEC engines are networked to a multi-function display their engine speed can be read very accurately.

The boat may be reaching 48-MPH speed over ground, but the engine speed is very likely faster than 5,400-RPM to accomplish this. Or, the data was taken while the boat speed was being increased by a very strong current.

quickenberger
Posts: 90
Joined: Sun Feb 05, 2017 8:48 pm

Re: 1986 Frontier 25 Twin 150-HP

Postby quickenberger » Mon Jul 20, 2020 3:27 pm

Current was probably around 2-3 mph. The tachometers appear correct and are a plug and play style hooked up to the main wire harnesses. When I'm out again this weekend I'll get a picture of the tachs and the fishfinder with the speed its showing. Does the boat speed of 34 mph and the engine speed of 4100 RPM correlate?

biggiefl
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Re: 1986 Frontier 25 Twin 150-HP

Postby biggiefl » Tue Jul 21, 2020 10:58 am

Yes but usually with 19" pitch props.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).