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Author Topic:   Two 13' engine questions...
KeysNole posted 12-06-2001 02:56 AM ET (US)   Profile for KeysNole   Send Email to KeysNole  
1. What is the heaviest motor that can safely be put onto a stock 13 transom? Does transom strength differ over the years? Although 13's are rated for up to a 40hp, an old 40 and a newer 4 stroke have huge weight differences, and I have seen a 70 hp on a stock transom.

2. What would average top speed on a 13 be with a 25 hp? I am looking to repower and can get a 97 Yamaha 25 at a great price, but am afraid I will lack decent speed with more than one person in the boat.

Any thoughts would be appreciated.

JBCornwell posted 12-06-2001 08:03 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Howdy, KeysNole. You have touched on a point that will become more and more important in the next few years: Engine weight.

Many boats are rated to carry horsepower that, in many 4 strokes, is too heavy for the boat to maintain balance. Montauks are prone to porpoise with anything over about 325# on the transom. That includes virtually every 4 stroke on the market over 60HP. Yet the boat is rated for 100HP.

Now THAT should start a good fight.

I had an OMC 25 on my last 13. It would maintain 25 knots (GPS) with two men and a boy aboard. It handled better than a similar boat with an OMC 40 (old cross-flow type), and I think it was nearly as fast, though I never measured the speed on the 40 horse version. Neither engine had T&T, so the foot angle was set and left alone.

Go for the Yammy 25. A great match for your boat.

Red sky at night. . .
JB :)

EasyE posted 12-06-2001 02:55 PM ET (US)     Profile for EasyE  Send Email to EasyE     
I find it hard to believe you got 25 knots with a stock 25hp on a stock 13. Im not sayin you didnt but it is just not what i've been hearing. I have been hearing about 25mph with a 25hp but 25knots is 29mph whats like wow, then you said with TWO men AND a boy!
Look at Clark Roberts sweet lookin 13' with 25hp yammy, it had jackplate, trim, fins, SSprop and a hell of a setback and he topped off at 30mph at his best.
Does any one else get 29mph with there 25hp??? Imagine the amount of gas you could save and money-EasyE
Bigshot posted 12-06-2001 03:33 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
With 1 or 2 small people I can see high 20's maybe 30. My 1982 35hp did close to 35 so compared to a modern, prop rated 25hp, I can see it. My 14' Carolina with a 30 Yamaha 2cyl did about 30(GPS) and that could have used more pitch.
JBCornwell posted 12-06-2001 05:35 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Howdy, EasyE. My gps read 25mph. I have been told that the gps system measures everything in nautical miles. That is why I claimed 25KT. The gps, when mounted in the truck, always measures speed at about 10% below speedo indicated speed (indicated 70 = gps 63.5).

I weighed about 175 at the time, my son about 200 and my grandson about 50. The engine was a box stock '85 Johnnyrude 25. Most of the measurements were taken on a 6-8" ripple with little wind. The tilt pin was set for best cruising speed at about 3500rpm (I think that was about 21). I have no idea what the prop pitch was; it came on the engine. The hull was clean as a whistle and waxed.

Red sky at night. . .
JB :)

newboater posted 12-06-2001 06:07 PM ET (US)     Profile for newboater  Send Email to newboater     
Whooa there JB,

I suspect your handheld GPS measures speed and distance in 'either' nautical miles or statute miles. You select which you want it to display. The GPS satellites just put out time and position pulses, the receiver does the rest. My Garmin prints MPH when using statute miles, and Kts when in using nautical miles.

That being said, KeysNole, my 13' has an old '75 40 hp. It has a really old style two piece lower unit that looks more like a big submarine than the sleek modern lower units. Even the prop looks funny compared to modern ones. Anyhow I get about 25 kts out of her (not quite 30 mph) with my 200 pounds self and a full 8-gallon gas tank. I recall the owner's manual said the motor weighs 150 pounds.

I suspect if you got a modern 25 or 30hp unit (which they say are rated at the shaft and not at the flywheel), you would beat me in top speed. But hey, who's in that big a hurry anyway?

Dave S.
San Diego

JBCornwell posted 12-06-2001 10:09 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Well, Newboater, from what you say, my GPS must have been reading statute miles rather than Nautical miles.

I don't have a problem with that, but why does it consistently claim my Mercedes Benz truck is really going so much slower than the Speedo claims??

I am slow to believe that this vehicle has such an inaccurate instrument.

Red sky at night. . .
JB :)

grandmufti posted 12-06-2001 10:45 PM ET (US)     Profile for grandmufti  Send Email to grandmufti     
Tire size could throw the speedo off on your truck.My old Astro van came factory with smaller diameter tires to help get the gear ratio I ordered for towing.It threw the speedo off about 5 miles at 60 mph.Made it read 65.
Bigshot posted 12-07-2001 10:08 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
JB my ML is pretty accurate, 63 kts is 70 I believe.
CarlRobert posted 12-07-2001 10:57 AM ET (US)     Profile for CarlRobert    
1962-13 sport, 2002 40 HP 4 stroke Merc(212 lbs) 20" shaft with pt&t, 4 blade ss Merc Trophy Sport 14 pitch prop.

With two adults (165 lbs & 210 lbs), 1 6 gal tank of gas-36 mph on gps.
With just me in the boat, WOT is too scary and the boat becomes unstable- a slight gust of wind will push the boat around!

Carl R

WantaWhale posted 12-07-2001 02:28 PM ET (US)     Profile for WantaWhale  Send Email to WantaWhale     
For reference, I get right at 25mph(solo) out of my 11' Supersport with a 20hp johnson. Thats with a Garmin gps. The foot is pushed all the way forward, so I might get more if I moved it back a notch or 2 but this gives a comfortable ride (no porpoising). Although I do not have a tach, I would say the rpms are only around 4500 (if that) and I can run it all day w.o.

WhalerHank posted 12-07-2001 08:45 PM ET (US)     Profile for WhalerHank  Send Email to WhalerHank     
I'm fairly new to Whalers having bought a 1963 a year ago. Restored and finished it up recently. The boat came with a 1970 Evinrude 50hp Lark 2 cylinder outboard weighing in at a SLIM 189 lbs. The moter preforms well enough but it is obviously to heavy for the boat in my opinion. It's not the hoesepower it's the weight only about 6" of freeboard at the stern and with only one person onboard the bow is somewhat light. In my opinion a 25 to 35 hp outboard would be perfect. That's what I'm looking for but It will be hard to find in a good used outboard.
Highwater posted 12-08-2001 07:15 AM ET (US)     Profile for Highwater    
Sufficient power is critical if you want to use the boat to pull up a slalom water skier or if you want to get on a plane with 6 people or 1200 pounds on board. Also, it is nice to be able to run 25 mph without pushing the engine to WOT. That's why I would not want anything less than a 40 hp engine on my 13. But if you and your family don't ski, and if you rarely have more than three people on board, a lighter engine would help make the boat sit better in the water (aesthetically) at idle speed.

I'm not sure how much fuel you would save by putting a lighter engine on the 13. I recently took my 1972 13-Sourpuss to Florida and went up and down Suwanee River, and from Manatee Springs State Park past Cedar Key and over to Crystal River. In all, I went 130 miles at 18-25 mph and my 1987 40 hp Johnson (which weighs 196 pounds) only burned 14 gallons of gas--almost 10 miles per gallon.

WHALERROB posted 12-08-2001 09:28 AM ET (US)     Profile for WHALERROB  Send Email to WHALERROB     
maxdevon posted 12-10-2001 04:29 PM ET (US)     Profile for maxdevon  Send Email to maxdevon     
I just put a 2002 Yamaha 40 H.P. 4-stroke on my restored 1981 whaler. I have a 12 gallon "whaler gas tank" as I'll call it mounted under the front bench seat which does place some weight forward. If you plan to carry 3 persons regularly, then the 25 H.P. is not enough motor, yet 25 H.P. would be good for 1 or 2 persons unless they were heavy set. I know people who have put 60 HP and agreed that was too much motor. I think 40 H.P. 4 stroke at 200 lbs is the absolute top end & mine handles it very nicely, & is well balanced. Definitely not too heavy in rear.

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