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Author Topic:   Re-Powering 13'--40HP or 25HP?
geok21751 posted 02-05-2002 08:29 PM ET (US)   Profile for geok21751   Send Email to geok21751  
Thanks to the Forum you steered me into a 1982 13' Sport. After 16 months of looking, I found this one owner Whaler in the grandson's garage. It had not been in the water in 12 years. It is equipped with a 1959 35HP Johnson, that runs well. Just not reliable. I use the boat for fishing, sailboat race crash boat and general putzing around on the 2000 acre lake where I live in Michigan. I sold my speedboat, so this may have to serve to pull kids on tubes and the occasional 135 lb skier.
My question is this; I was looking at the 40HP 4 cycle, but was warned of the engine weight, and the possibilty of over RPM'ing the engine. It has been suggested that I consider the 25 HP Mercury 4 cycle, Bigfoot (highthrust). The claims are that it will have all the power and speed that I need. Any opinions or experience here? Comments on the Honda vs. the Mercury are also welcome. Thanks in advance!
JBCornwell posted 02-05-2002 09:25 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Howdy Geok.
I agree that the Merc 40 is too heavy. On the other hand 25 may not tow a skier.

The Honda BF30 and the Yamaha F25 are both lighter than the 40s and the Merc Bigfoot 25.

I think a bigfoot or a high thrust would be a mistake on a 13. The bigger gearbox adds drag. Those engines are intended for pontoons and auxilary applications, not light runabouts.

I would go with the Honda BF30. At 152lb it is lighter and more powerful than the Merc Bigfoot 25. The Yamaha F25 is even lighter at 136lb.

Red sky at night. . .
JB :)

SteveC posted 02-06-2002 06:36 PM ET (US)     Profile for SteveC    
I vote for the 40 hp for water skiing. The engine is heavy, but moving the fuel forward and using a lighter battery could save the 50 lbs from the back of the boat. I am looking at the f25 and f40, but I won't be water skiing.

Last time I checked, the honda was more $ than the yamaha, and the mercury bears a striking simularity to the yamaha.

I've ran a 50 Honda, the only problem I had was remembering if it was running or not (very quiet).

Salmon Tub posted 02-06-2002 08:32 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
I don't quite understand what you mean by overreving the engine, the whole idea is that with a higher horse motor, you can use a higher pitch prop which will give you more top end speed without lugging the engine because of the higher horsepower. At the same time, you could get a second low pitch prop to pull askier. As far as weight goes one of my buddies has an old 13 with a 40 horse honda that he uses all over San Francisco bay, and so far has taken the ocassional bit of water over the transom but not even close to enough to cause any major worries. He also keeps a 20 gal. bait tank there as well.
andygere posted 02-07-2002 02:33 PM ET (US)     Profile for andygere  Send Email to andygere     
If you are going to pull skiers with a 13, don't get less than the 40. Take a look at the Tohatsu/Nissan 40 hp 2-stroke. It's light weight, 3 cyl, less expensive than the big 3 and still available with power T/T in both 20" and 15" lengths. A friend of mine mail-ordered a smaller model from these guys, at rock bottom prices.

Duncan posted 02-16-2002 10:56 AM ET (US)     Profile for Duncan  Send Email to Duncan     
I repowered my 13 from a Johnson 35 to a used 80s Merc 40. very stupid move. I didn't check to see if it had the "half-cock" tilt allowing it to run in to run in shallow water. I use the boat for fishing and duck hunting and need to run in the swallows. Now I'm screwed. Moral of the story....check features!
Bigshot posted 02-19-2002 03:18 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You are not screwed. Use a block of wood.
jimh posted 02-20-2002 12:01 AM ET (US)     Profile for jimh  Send Email to jimh     
I am somewhat skeptical about the advice offered for this re-powering.

First, the 40-HP 4-stroke is probably too heavy. What is the weight? The 13-foot hull was designed in the 1950's when outboard engines were lighter.

The comment that a 40-HP engine could "over rev" on a 13-foot hull is a strange one. You adjust the propeller to control the maximum engine speed. (See for some background.) When fitted with the proper propeller, a 40-HP will be able to produce greater boat speed, not excessive crankcase speed.

Second, the "big foot" gear case designs are intended for pushing slow, heavy boats. The 13-foot Whaler is a rather light, planing hull, nothing at all like the boats intended for the big-foot lower units. The big-foot engines are able to turn larger diameter props and are usually gearer lower to develop more torque and slower prop shaft speeds.

A 1959 35-HP engine is probably about the same actual power as a current model rated as a 30-HP.

Look at some 13-foot hulls repowered with modern engines and note their static trim.
Compare and (42-2)

PMUCCIOLO posted 02-21-2002 05:00 AM ET (US)     Profile for PMUCCIOLO    
My brothers and I have owned four (or five) 13's. The oldest of them had steering via a joystick-type setup and had a 33HP Evinrude, the latest of them has a 40HP 4S Mercury (my current 1999 GLS). I recommend the 35 to 40 HP range in a two-stroke engine for the application you have described. If I remember correctly, the 4S Mercury 40 weighs either four or eight pounds more than the 2-stroke model. What you lose is hole shot. If you're going to ski or wakeboard, the two-stroke will give more of that, as every stroke is a "power" stroke. The engine's RPM maximum is dictated by the propeller and trim angle of the engine. I recommend power trim and tilt, as the 13 is a bit trim sensitive, and, when trimmed out properly, will fly with the correct motor and prop combination. If I can be of any further assistance, please feel free to call me (386)767-1933 or e-mail at: Good luck!
Whalerdan posted 02-21-2002 08:29 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
I was looking at those posts Jim just mentioned and I like the 13 with the pull start Johnson. The simplicity is great (KISS). It got me thinking. Could one have power tilt, on a pull start motor, by running it off the rectifier?
Bigshot posted 02-21-2002 10:58 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
maxdevon posted 02-21-2002 01:36 PM ET (US)     Profile for maxdevon  Send Email to maxdevon     
I went the 40-HP 4-stroke Yamaha Route but I have the 20" transom (1981 hull) The motor is definitely not too heavy (195 lbs approx for the 20" shaft. Yamaha offers the 15" shaft for the 40-HP 4-stroke). I do have a 12 gallon fuel tanl mounted under the front seat though to shift weight forward, but I like the setup. The battery box is under the console. You will not over rev the motor with a 13 or 14 pitch prop. You will with an 11 pitch. I'll send you some photos via email. Good Luck
maxdevon posted 02-21-2002 09:03 PM ET (US)     Profile for maxdevon  Send Email to maxdevon     
Thought I'd pass along some hard numbers from my experimenting:

For my 40 HP 4-stroke Yamaha, I had a few friends who loaned me props to experiment with.

The 1st prop was a 10 1/4" x 15 pitch Stainless prop, the boat was very slow to plain, but very fast on top end. Max RPM was 4600. I should be getting at least 5500 RPM.
Prop #2 was a 10 5/8" x 12 pitch Aluminum. Don't let anyone tell you a 4-stroke is slow out of the hole. They've just never had the right prop. My 13' literally leaped onto plain as fast as anything I've ever been in. Guess what, I could overrev to 6000 RPM at 2/3 throttle.

So, I have Prop #3 which is Aluminum 10 1/4 x 14 pitch and it works just about right. I get about 5400 RPM at Max throttle, fast top end & OK out of the hole. I admit I wanted as fast as I could get but didnt want to over work the motor.

The 15" yamaha 40 HP 4-stroke only weighs 181 lbs which is a lot better than the other 40HP 4 strokes.

Bigshot posted 02-21-2002 09:51 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
181 is Ok in my book but is pushing the envelope. Like I posted before a 1971 Evinrude 25hp weighed 81lbs but to todays standards is probably only 18-20hp. Therefore I believe a 30hp modern engine is a great package on a classic 13. My 1982 Johnson 35hp was plenty for a 13 and would be equiv to about a 30 today. Keep the weight down because honestly the extra couple MPH from the 40 aint worth the money or weight in my book. The 13 design(like the 17)is an efficient hull. Efficient hulls will show slight MPH gains with additional HP. Where it comes into play is when weight is added. You guys would be disappointed if you ran a 30hp with your 40 with a single won't "dust" them.

Just my $.02.

maxdevon posted 02-23-2002 01:26 PM ET (US)     Profile for maxdevon  Send Email to maxdevon     
I can't disagree with Bigshot at all. 40 is pushing th envelope on weight & cost versus what you get out of it in performance.
Bigshot posted 02-23-2002 01:38 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
PS: If you want to go fast, buy a 15 with a 70hp. Actually a 15 with a 40 will be faster than a 13 due to hull design. My friend had a 1982 15 with a 35hp Evinrude w/bottom paint. I had a new 13' with a 35hp Johnson and no bottom paint and he was faster out of the hole and Wot was about 3mph faster. With that said I have seen a 13 Supersport with a 3cyl 60hp Johnson(250lbs). It sat pretty low but I did not talk to him because he was wearing "buttfloss" and I just could not approach him. I hope this was boring enough. Just FYI.
jimh posted 02-23-2002 03:22 PM ET (US)     Profile for jimh  Send Email to jimh     
My wife's aunt used to have an old 13-Sport with a 25-HP Evinrude. The engine was a pull-start and had no power trim. I don't think there was a battery in the boat. The boat was on a lake in northern Canada, so during the short summer there was daylight until 10 p.m. and you really didn't need NAV lights.

I do recall that you could water ski behind this little rig, although probably not exactly like you could behind a Ski-Nautique.

At the end of the season (3rd week of August), the motor was loosened from the transom and carried into the garage. The boat was hauled up on the beach, flipped upside down, and covered with a tarp for the 8-month Canadian winter.

Things were simpler back then, eh?

AZdave posted 02-24-2002 02:08 AM ET (US)     Profile for AZdave  Send Email to AZdave     
I changed out the old 40HP that came with my '68 for a Yamaha two stroke 30HP which their website says weighs 132 pounds. It works great for tubing, and will plane kids or adults in the 150 pound range when using two skis. It will not plane big guys (200+) at all. I think the 40HP might be better for skiing as it would get on plane more quickly. The transition from plowing to planing seems to cause the most trouble for people with little skiing experience. This might not be true if you are a lighter driver than I am. I guess I could lose 40 lbs. and put any motor I want on the boat!! Dave
mgrl posted 03-06-2002 08:28 AM ET (US)     Profile for mgrl  Send Email to mgrl     
I just discovered this great site while looking for information about what to do with a 1970 13' that has the 1968 40hp Evinrude that my dad bought when I was a kid. They've been garaged for 10 years and I want to rig it reliably or get it ready to sell. The boat is in great shape, the motor was skittish the last summer used. I'll be using the boat to toodle around in coastal marshes. Getting to the marshes will need some speed, but I don't need speed/power for skiing/pulling). The new 40hps are prohibitively expensive. Any thoughts on smaller motors for this use?
Bigshot posted 03-06-2002 10:15 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I'll say it agian...I think a 30hp is perfect.

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