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Author Topic:   SPORT 13: Transom Height

Juggo posted 04-01-2006 06:48 PM ET (US)
I'm looking into getting a new motor for my 1980 13 foot Whaler Sport. I think it needs a long shaft since the transom measures about 20-21 inches, but Whalers seem so low, I was wondering if anyone knew for sure.
[IMGhttp://i16.photobucket.com/albums/b32/Juggo/whaler_transom.jpg[/IMG]
I went to a boat show today and found good deals in my price range on a 25 horse 2 stroke Mercury or a 20 horse Honda 4 stroke. There's like 50 pounds difference between a 2 and 4 stroke engine. Should I be concerned about the weight on the back of this older boat. I'm leaning toward the Honda, I like the idea of a 4 stroke, but wonder if 20 HP is enough to allow me to jump waves ;) Could a 25 horse 4 stroke Mercury be too heavy?
Juggo posted 04-01-2006 07:02 PM ET (US)
[img]http://i16.photobucket.com/albums/b32/Juggo/whaler_transom.jpg[/img]
tucker posted 04-01-2006 07:07 PM ET (US)
I've got a 40hp four stroke on my 13'. Couldn't be happier with the performance. Put a "whale tail" on the anti cavitation plate and the nose goes right down at probably no more than 5 kts.
Juggo posted 04-01-2006 07:15 PM ET (US)
40 is out of my price range. But your saying a 25 hp 4 stroke is not a problem. What year is your boat?
Do your motor have a long shaft on it?
Mumbo Jumbo posted 04-01-2006 09:51 PM ET (US)
I would recommend a Yamaha 25hp four stroke with power trim and tilt. It is plenty of engine for the 13 unless you are into water skiing. It needs to be propped with a good cupped stainless prop for optimal performance. Email me if you want specifics.
jimh posted 04-01-2006 11:48 PM ET (US)
Information on transom height is available in the REFERENCE section.
Juggo posted 04-02-2006 02:55 PM ET (US)
What about the shaft size? Whalers use long shafts right?
Tom W Clark posted 04-02-2006 03:26 PM ET (US)
A 1980 Sport 13 uses a 20" shaft motor. 13 footers with blue interiors use 15"
shaft motors.
pglein posted 04-03-2006 11:44 AM ET (US)
Let me clear up some confusion. Transom height and shaft length are essentially the same thing. A boat with a 20" transom, will take an engine with a 20" shaft. The fact that the boat sits lower in the water has nothing to do with it. When you get it up on a plane, the entire transom will be out of the water.
As for your engine questions, I would consider a 25 horse only if you're going with a 2 stroke. Weight hanging on the transom of a 13' is a huge factor in it's performance. With a 200# 25 horse, you'll have trouble getting on a plane.
I've had a 30hp Johnson, a 40hp Evinrude, a 9.9hp Nissan, a 25hp Suzuki, and a 30hp Yamaha on my 1971 13' Whaler over the years; all of them 2 stroke. Both 30hp engines have been excellent compromises. They were light enough to ride properly, and gave good performance. The Yamaha 30 (my current engine) works fine unless I'm carrying two adult males, two full tanks of fuel, and attempting to plane into a stiff breeze. In those cases, I have to shift weight forward. I top out at about 25 knots with just me in the boat. I cruise at about 20. The 40 was about the most weight I'd put on that boat. That engine was a 1988 and so it weighed no more than 190#. Mine had the 15" transom, and I had problems keeping water from coming over the transom with that engine. Obviously performance was stellar, with top speed of about 35 knots and lighning quick planing. The 25 was fine for one person, but had trouble planing with two sitting in the rear seat (passenger had to move forward to get up). With more than two, it would plane (due to better weight distribution), but it was a soft plane; sort of plowing through the water, but slightly elevated. The 9.9 was the most interesting engine. It would plane easily with one person, and barely plane with two. I never clocked the speed, but obviously it was slow. However, it demonstrated how critical engine weight is in the performance of the boat.
If you're considering a 25, you should step up to a 30. They usually weigh the same, and since weight is so critical, you want to squeeze as much power out of the weight as possible. Obivously two strokes are getting to be harder to come by, but I the tradeoffs of a 4 stroke just aren't worth it for a small boat like a 13' Whaler. They simply weigh too much for that boat.
tucker posted 04-04-2006 09:19 AM ET (US)
my 13' has a 21" transom. The forty 4 stroke weighs 212 lbs.It is not too heavy for the boat. I have had it in the intercoastal for seven years and no problems with water ingressing the boat. That is seven years of experience with that particular setup. I am not a marine engineer. I am not an expert. Just a very happy owner with a forty hp four stroke stuck on the back of a 13' whaler with a 21" transom.
As for tradeoffs and the forty being too much weight I guess that is a matter of opinion and what you are trading off. I traded off nothing. I got exactly what I wanted.
Tom W Clark posted 04-04-2006 10:20 AM ET (US)
No tucker, your boat has a 20" transom, not a 21" transom. Transom height is just that, height, not length.
Measure the vertical distance between the keel and the top of the transom. Measure this distance perpendicular to the keel, not along the face of the backward sloping transom.
It's the difference between the the altitude and the hypotenuse of a right triangle.
tucker posted 04-04-2006 08:28 PM ET (US)
mea culpa. mea culpa. mea maxima culpa.
you are right. It is only twenty inches.
Myth Busted!

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Author	Topic: SPORT 13: Transom Height
Juggo	posted 04-01-2006 06:48 PM ET (US) I'm looking into getting a new motor for my 1980 13 foot Whaler Sport. I think it needs a long shaft since the transom measures about 20-21 inches, but Whalers seem so low, I was wondering if anyone knew for sure. [IMGhttp://i16.photobucket.com/albums/b32/Juggo/whaler_transom.jpg[/IMG] I went to a boat show today and found good deals in my price range on a 25 horse 2 stroke Mercury or a 20 horse Honda 4 stroke. There's like 50 pounds difference between a 2 and 4 stroke engine. Should I be concerned about the weight on the back of this older boat. I'm leaning toward the Honda, I like the idea of a 4 stroke, but wonder if 20 HP is enough to allow me to jump waves ;) Could a 25 horse 4 stroke Mercury be too heavy?
Juggo	posted 04-01-2006 07:02 PM ET (US) [img]http://i16.photobucket.com/albums/b32/Juggo/whaler_transom.jpg[/img]
tucker	posted 04-01-2006 07:07 PM ET (US) I've got a 40hp four stroke on my 13'. Couldn't be happier with the performance. Put a "whale tail" on the anti cavitation plate and the nose goes right down at probably no more than 5 kts.
Juggo	posted 04-01-2006 07:15 PM ET (US) 40 is out of my price range. But your saying a 25 hp 4 stroke is not a problem. What year is your boat? Do your motor have a long shaft on it?
Mumbo Jumbo	posted 04-01-2006 09:51 PM ET (US) I would recommend a Yamaha 25hp four stroke with power trim and tilt. It is plenty of engine for the 13 unless you are into water skiing. It needs to be propped with a good cupped stainless prop for optimal performance. Email me if you want specifics.
jimh	posted 04-01-2006 11:48 PM ET (US) Information on transom height is available in the REFERENCE section.
Juggo	posted 04-02-2006 02:55 PM ET (US) What about the shaft size? Whalers use long shafts right?
Tom W Clark	posted 04-02-2006 03:26 PM ET (US) A 1980 Sport 13 uses a 20" shaft motor. 13 footers with blue interiors use 15" shaft motors.
pglein	posted 04-03-2006 11:44 AM ET (US) Let me clear up some confusion. Transom height and shaft length are essentially the same thing. A boat with a 20" transom, will take an engine with a 20" shaft. The fact that the boat sits lower in the water has nothing to do with it. When you get it up on a plane, the entire transom will be out of the water. As for your engine questions, I would consider a 25 horse only if you're going with a 2 stroke. Weight hanging on the transom of a 13' is a huge factor in it's performance. With a 200# 25 horse, you'll have trouble getting on a plane. I've had a 30hp Johnson, a 40hp Evinrude, a 9.9hp Nissan, a 25hp Suzuki, and a 30hp Yamaha on my 1971 13' Whaler over the years; all of them 2 stroke. Both 30hp engines have been excellent compromises. They were light enough to ride properly, and gave good performance. The Yamaha 30 (my current engine) works fine unless I'm carrying two adult males, two full tanks of fuel, and attempting to plane into a stiff breeze. In those cases, I have to shift weight forward. I top out at about 25 knots with just me in the boat. I cruise at about 20. The 40 was about the most weight I'd put on that boat. That engine was a 1988 and so it weighed no more than 190#. Mine had the 15" transom, and I had problems keeping water from coming over the transom with that engine. Obviously performance was stellar, with top speed of about 35 knots and lighning quick planing. The 25 was fine for one person, but had trouble planing with two sitting in the rear seat (passenger had to move forward to get up). With more than two, it would plane (due to better weight distribution), but it was a soft plane; sort of plowing through the water, but slightly elevated. The 9.9 was the most interesting engine. It would plane easily with one person, and barely plane with two. I never clocked the speed, but obviously it was slow. However, it demonstrated how critical engine weight is in the performance of the boat. If you're considering a 25, you should step up to a 30. They usually weigh the same, and since weight is so critical, you want to squeeze as much power out of the weight as possible. Obivously two strokes are getting to be harder to come by, but I the tradeoffs of a 4 stroke just aren't worth it for a small boat like a 13' Whaler. They simply weigh too much for that boat.
tucker	posted 04-04-2006 09:19 AM ET (US) my 13' has a 21" transom. The forty 4 stroke weighs 212 lbs.It is not too heavy for the boat. I have had it in the intercoastal for seven years and no problems with water ingressing the boat. That is seven years of experience with that particular setup. I am not a marine engineer. I am not an expert. Just a very happy owner with a forty hp four stroke stuck on the back of a 13' whaler with a 21" transom. As for tradeoffs and the forty being too much weight I guess that is a matter of opinion and what you are trading off. I traded off nothing. I got exactly what I wanted.
Tom W Clark	posted 04-04-2006 10:20 AM ET (US) No tucker, your boat has a 20" transom, not a 21" transom. Transom height is just that, height, not length. Measure the vertical distance between the keel and the top of the transom. Measure this distance perpendicular to the keel, not along the face of the backward sloping transom. It's the difference between the the altitude and the hypotenuse of a right triangle.
tucker	posted 04-04-2006 08:28 PM ET (US) mea culpa. mea culpa. mea maxima culpa. you are right. It is only twenty inches. Myth Busted!