13' Boston Whaler with Merc 35

[KeltonKrew]

I'm re-doing my 13'whaler (mid sixties, 15" transom). I've been using it for fishing and decided I'm tired of wearing camo so people won't recognize me....brought it home today and gutted it.<br />Here's my question.<br /><br />I know this is a 15" transom, but the previous owner mounted the Merc 35 (20" motor) to the boat....Best I've ever been able to run is 27mph (gps) with a 10 1/8 x 15 SS prop and a whale-tail on the ventilation plate. The ventilation plate is roughly 2.5" - 3" below the bottom of the hull....I'll be putting on the CMC power tilt/trim (5" setback - maybe 6") and raising the ventilation plate to start with about 1" ABOVE the bottom of the hull...<br /><br />How much more top end and performance should I expect by moving the motor up and get it from being a parasitic drag by being too low!<br /><br />thanks guys!

 

[cobra 3.0]

Re: 13' Boston Whaler with Merc 35

Wild *** guess...3 to 5 miles per hour. Just taking off your whale tail should gain you 2 mph.

 

[JB]

Re: 13' Boston Whaler with Merc 35

Ahoy, KK.<br /><br />My '75 and '80 BW 13s (both 20" transoms)performed as follows:<br /><br />JohnnyRude 25: No hydrofoil, 25mph GPS.<br /><br />JohnnyRude 40: No hydrofoil, 42mph GPS<br /><br />JohnnyRude 50: No idea what it would have done at WOT. At 45mph it scared me so bad I never opened it up again. Switched back to the 25.<br /><br />With a setback and proper "X" dimension you should expect 35-38mph from your 35. Take the foil off, it offers no benefit on a well balanced 13.

 

[Old Jarhead]

Re: 13' Boston Whaler with Merc 35

JB...<br /><br />What do you think would be the difference of MPH [WOT] and fuel consumption of a 13' Whaler w/25hp [my set up] with and without a hydrofoil?

 

[JB]

Re: 13' Boston Whaler with Merc 35

Ahoy, Gyrene.<br /><br />Unless your 13 is tail-heavy from loading, I would expect a hydrofoil to shorten plane time, reduce minimum plane speed, slightly increase fuel usage at cruise and slightly reduce WOT speed.

 

[Old Jarhead]

Re: 13' Boston Whaler with Merc 35

JB...<br /><br />After my post I figured I'd just take a run down to the water and see for myself how much the difference was.<br /><br />First, I ran 5800 RPM with the foil. The result was about 22-22.5 MPH [GPS]. Back to the dock, removed the foil and ran again. This time I got 25-25.5 MPH @ 5800 RPM.<br /><br />Close to 15% difference in speed. I have to assume the fuel difference will be similar.<br /><br />The bottom line is the hydrofoil stays off.<br /><br />'03 130 Boston Whaler Sport powered by a '03 25hp 4 stroke Merc. Engine mounted on the second set of holes [from the top]. Normal load with a Minn-Kota Tidewater bow mount trolling motor & battery.

 

[richg99]

Re: 13' Boston Whaler with Merc 35

I added a CMC PT35 to a prior boat since the motor did not have tilt/trim. The hydraulic setback/t/t ( and having my mechanic raise the motor ABOVE the level of the hull)...greatly increased speed; and ability to get up on plane. I did additionally add a Whaletail, inspite of the probable loss of high end speed, since I had to get her up in 12/15 inches of water most of the time ( Texas salt flats). I didn't mind losing a little top end speed as a trade off for the increase in planing ability. After reading a lot here, however, I might have been better off fore-going the whaletail and putting on Smart-Tabs or other brands of tabs. RichG

 

[Selles]

Re: 13' Boston Whaler with Merc 35

I have B.Whailer 13ft. 25hp , What is the propeller combination that you use to reach 22- 25 mph ,JB.

 

[JB]

Re: 13' Boston Whaler with Merc 35

I don't know, Selles. I never had reason to check it.

 

[Jdeagro]

Re: 13' Boston Whaler with Merc 35

Kelton;<br /><br />Your motor shaft is too long, and the hydrofoil is causing even more issues than normal because it is sitting deep in the water. I am not a fan of hydrofoils and have a proprietary interest in Smart Tabs. Raise the motor, and remove the hydrofoil, then see what happens.

 

[KeltonKrew]

Re: 13' Boston Whaler with Merc 35

Kelton;<br /><br />Your motor shaft is too long, and the hydrofoil is causing even more issues than normal because it is sitting deep in the water. I am not a fan of hydrofoils and have a proprietary interest in Smart Tabs. Raise the motor, and remove the hydrofoil, then see what happens. <br />

That's what I'm doing now.. Motor is off the boat (boat is completely gutted now). After painting, etc I will be putting on the CMC PT-130 which will raise my engine up and give a 6" setback. foil is off the motor and I need to fill the holes in the plate now. I'll hopefully have it all back together by April.

 

[Jdeagro]

Re: 13' Boston Whaler with Merc 35

Hope to hear from you when your in the water - good luck!