1978 SPORT 15 with 40-HP

Optimizing the performance of Boston Whaler boats
Deewazz
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Joined: Mon Jun 06, 2016 7:22 pm

1978 SPORT 15 with 40-HP

Postby Deewazz » Wed Jun 22, 2016 9:20 am

My 1978 Sport 15 has the wrap-around seating and rail configuration. I plan to install a 2000 Mercury 40-HP FOURSTROKE engine with carburetors. I boat on a rather small lake, and have no compulsion for speed. What can I expect for full-throttle performance with two adults and little else aboard?

macfam
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Re: 1978 15 sport perfomance with 40 hp

Postby macfam » Wed Jun 22, 2016 4:48 pm

Assuming that the set-up is correct. (Height on transom, reasonable prop, engine running to specifications) experience tells me 25 to 28 mph top speed.

Dontpokethebear
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Re: 1978 15 sport perfomance with 40 hp

Postby Dontpokethebear » Fri Jun 24, 2016 11:36 am

Yes, I just sold 1980 15-footer with 2004 TOHATSU 40, and your numbers are right-on. The boat hit 30-MPH a couple of times with a very light load and help from wind and current. Cruise speed with me, wife, two younger kids, beach gear, and dog would be around 18 to 20-MPH at 4800-RPM. Those numbers are at the beach, so yours may be a little different, due to different water conditions.

jimh
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Re: 1978 SPORT 15 with 40-HP

Postby jimh » Fri Jun 24, 2016 11:52 am

I had a very light weight 1976 SPORT 15 hull with a very light Mercury 500 50-HP engine (powerhead rated horsepower). The best boat speed was 34-MPH. For a SPORT 15 with 40-HP (propeller shaft-rated) and a heavier engine, the estimates of 30-MPH top-speed sound very reasonable.

Assume the 50-HP power-head rated engine was making about 45-HP at the propeller. Assume the boat weights were identical. The speed would reduce by the ratio of horsepower to the 0.5-exponent:

34-MPH x ( 40-HP/45-HP )^0.5 = 32-MPH

Add an allowance for increase in weight which reduced speed, and 30-MPH sounds attainable.

Deewazz
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Re: 1978 SPORT 15 with 40-HP

Postby Deewazz » Fri Jun 24, 2016 12:55 pm

Thanks. It's just about what I figured. I am running a 14-pitch aluminum 3-bladed propeller recommended apparently based on the boat specifications. I'll be happy with that level of performance. I'll post back the actual data when I get her in the water. I'm still hunting for some used controls.

LCnSac
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Re: 1978 SPORT 15 with 40-HP

Postby LCnSac » Fri Jun 24, 2016 9:56 pm

For a comparison, I have a 2005 150 Sport which weights about 300 lbs. more than your Sport 15. I have a 60 HP Mercury 4S that weighs about 265 lbs, so I'm probably close to 350 lbs more without personnel. Yesterday I took it out for the first time since my water trial at purchase. I was in 10 mph winds against me and 1' waves, and my best was 33 mph @5800 PRM with two of us on board, maybe 350 lbs. between us. In the water trial I got 34 mph with two of us in calm conditions. In neither case did I experiment much with trim, but it's safe to say I'll be either side of 35mph regardless of trim and passengers. I think the estimates given are probably quite accurate.

I had to look up the weight of your Sport 15, and was shocked at how much lighter it is than mine. I am not sure why, other than the post classic hulls seem to be a little larger in width and depth.

macfam
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Re: 1978 SPORT 15 with 40-HP

Postby macfam » Sat Jun 25, 2016 9:14 am

The new 150's (I have a 150 Montauk) weigh SO much more than the Classic versions. The 150 Montauk (dry) is a whopping 950 pounds!!
That (I believe) is the same weight as the 17 Montauk! And, the 150 Montauk is 4" WIDER then the older Montauk.
It amazes me that with a Mercury 60 EFI 4-stroke Bigfoot, it hits a solid 35 mph with my wife and I. (14" SS Vengeance prop)

For a 15.5" boat, it has an incredibly dry ride.

LCnSac
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Joined: Tue Mar 29, 2016 7:42 pm

Re: 1978 SPORT 15 with 40-HP

Postby LCnSac » Sat Jun 25, 2016 12:32 pm

The Sport 15 may be the coolest Boston Whaler ever built, but for me as a primarily fresh water fly fisherman who is always standing and casting, the initial stability is not adequate.

[Changed topic and began to discuss other models of Boston Whaler boat. I have returned these remarks to the author who is welcome to present is comments on these other boats in a new thread.--jimh]

Deewazz
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Re: 1978 SPORT 15 with 40-HP

Postby Deewazz » Sat Jun 25, 2016 7:38 pm

I agree with the last post. I've had 3 15's: a basic hull, a Center Console, and now the Sport with the wrraparound seat setup. I've had 8 Whalers before this in my life, and this is hands down my favorite. At age 73, this is my ultimate and last Whaler. I am just getting into flyfishing, and the boat is perfect for that. I can haul my grandkids around on a tube, and in a few years - on kneeboard or beginner skis. I'm set for the rest of my days thanks to Boston Whaler. (Now- if I could ONLY find the correct fuel line connector to the motor for my 2000 Merc 40 4-stroke....)

Deewazz
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Re: 1978 SPORT 15 with 40-HP

Postby Deewazz » Fri Aug 05, 2016 1:18 pm

Just ran my Whaler up and used my GPS to calculate. With 6 gallons of fuel, standard battery, my son and I both at 205 lbs: GPS showed 34.7 mph, and I trimmed up a little, and gained a bit more speed, but didn't record the GPS. I'm eminently satisfied with this setup.

jimh
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Re: 1978 SPORT 15 with 40-HP

Postby jimh » Fri Aug 05, 2016 10:47 pm

Your results with a 40-HP on your 1978 SPORT 15 boat correlate with the speeds I recall with mine. I think your engine and propeller set up are close to optimum.

The lighter weight of the early models of the SPORT 15 are probably due to use of less wood reinforcement in the cockpit deck and use of a generally lighter laminate lay-up. I suspect that after a few years of production of the classic 15-foot hull that Boston Whaler made have increased the laminate lay-up schedule, adding weight. They also put more wood reinforcement into the cockpit deck, also adding weight.

Deewazz
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Re: 1978 SPORT 15 with 40-HP

Postby Deewazz » Mon Aug 08, 2016 8:38 pm

Thanks, Jim for corroborating my data. I agree with your views on the 15: in my opinion, it's the very best of designs.

hopewar
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Re: 1978 SPORT 15 with 40-HP

Postby hopewar » Mon Mar 13, 2017 2:32 am

I agree with the second comment about that.
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