Seaway 19 repower; sizing considerations?

Jangles

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I've read through what threads I could find, but there hasn't been a tremendous amount of discussion about what works.

I've bought a boat: 1985 Seaway 19 currently rigged with, believed to be original, "tower of power" Mercury 90hp which hasn't run in years. I can probably get it running with a carb kit or three. Has frozen steering and some other quirks that are workable but I plan on repowering for fuel economy if nothing else. It weighs in at a bit over 300lbs

I also have a 2006 Honda BF50, at bit more than 200lbs.

Awesome.... or is it? Now I'm having second thoughts that the 50hp isn't going to efficiently push the boat.

I don't need or want to go 30kts, but with 4 adults and gear will I be able to cruise around 20? 15? I've used various online calculators with little success.

Should I try to sell the 50 and track down a 70?

I see similar boats rigged with 40-115hp and I can't get a read on what performance is truly being reached. A lot of "pushes it well" and "goes great." Anyone have real numbers? 4 strokes have different performance profiles than 2 strokes, so that's a consideration as well.
 

Bill_N

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50hp seems light on a 19 footer especially if it had a 90 on it. What is the max hp on the hull? I'd stay around 75% of that.
 

Eastporter

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I originally had a newer 50 hp Johnson 2 stroke on my 20' Eastporter and I was not happy with the performance with more than 1 person on board. I went with an 80 hp Suzuki 4 stroke and it was well worth it. It is quiet, excellent fuel economy, and with electronic fuel injection it is as reliable as my car.
I would sell the 50 hp Honda and put the money towards a 4 stroke in the 70-90 hp range. Suzuki has a free 6 year warranty if you buy new.
 

Jangles

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Yes, it is light. The boat supposedly is 1200lbs, loaded I'm thinking 2500. It is dry, no wet foam in the hull. It's obviously semi-displacement. Center console, no hard chines, and relatively small skeg. Pretty common hull similiar to the GM, Midland, etc. from my research (though I'm far from an expert).

I think it was rated for 90, but there isn't a tag so I can't be sure. I heard 70% of max, so that again puts me at 70hp... which I suspect gives a 30mph top end. I'm just using it for island hopping and bay cruising; not actually trying to get anywhere. And the GF is going to be running it some so I'd rather keep it conservatively powered. That said, I don't want to have a complete dog.
 

Eastporter

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The 20' Eastporter could be a cousin to the 19' Seaway. Very similar hull.
 

Jangles

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FYI, the BF50 is a 4 stroke, as are all Hondas, in case you didn't know.

Also it seems the HP ratings of old 2 strokes (crank) do not equal modern ratings (prop). Supposedly the older 2s are up to 10% off on top of being measured at the crank, so that old 90 may have actually been putting out closer to 75 at the wheel. The new Honda would be a true 50. So 70% of 75hp is 52.5, perhaps close enough.

I'm trying to convince myself it's going to be good enough.... and it probably isn't.
 

BOSBoatMan

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Jangles measure twice cut once

I overpowered my little 16 Leblanc with a 90 ETEC. When I'm running at the boat's "happiest" speed and attitude I'm not even running 4000 rpms. It's really nice to know...that even though I don't need to get more out of it, if I want it, I can have it.
 

Bill_N

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I've had both 2 stroke and 4 stroke. A 2 stroke produces more torque at lower rpms than a 4 stroke so it will pop you up on plane quicker. The HP you're losing or gaining is at the upper end of the rpm range where you will rarely use it.
 
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Bill

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From what ive seen a lot of those 19s have 70 johnsons..My buddy bought one a year or so ago with a 70 and it went along fine with 2 of us in it.
 

Bill

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then again.. maybe call this guy and see what he is getting for #s

1996 Eastern Classic 18 w/'03 Yamaha F50

I've read through what threads I could find, but there hasn't been a tremendous amount of discussion about what works.

I've bought a boat: 1985 Seaway 19 currently rigged with, believed to be original, "tower of power" Mercury 90hp which hasn't run in years. I can probably get it running with a carb kit or three. Has frozen steering and some other quirks that are workable but I plan on repowering for fuel economy if nothing else. It weighs in at a bit over 300lbs

I also have a 2006 Honda BF50, at bit more than 200lbs.

Awesome.... or is it? Now I'm having second thoughts that the 50hp isn't going to efficiently push the boat.

I don't need or want to go 30kts, but with 4 adults and gear will I be able to cruise around 20? 15? I've used various online calculators with little success.

Should I try to sell the 50 and track down a 70?

I see similar boats rigged with 40-115hp and I can't get a read on what performance is truly being reached. A lot of "pushes it well" and "goes great." Anyone have real numbers? 4 strokes have different performance profiles than 2 strokes, so that's a consideration as well.
 

skinny vinyl

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19 seaway

i just repowered a 19 seaway with a 50 yamaha it had a 70 goes great with the 50
 

Jangles

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Thanks for the responses.

I have noted a lot of them have 70s. The PO of this hull said the boat absolutely flew with the 90...

That Eastern on craigslist, with the F50 is about what I would have (though the picture doesn't look like a yammi). I did email the guy just now, we'll see what he comes back with.

The 18 Eastern Center console currently sold new, which I believe is roughly the same hull, has a recommendation of 50-70 according to the website. That's promising.

I'm trying not to dump a lot of money into the project, so having to bump up in HP "just to have" isn't really motivating. I'm not using the boat that often or in areas where I suddenly will need to get somewhere.

I think it'll be alright. I won't have the boat laden with heavy gear and it's a fair-weather boat only. Worst case I'll have to re-power again down the road.
 

Jangles

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RE: The Eastern with the F50:

"I'm not a numbers guy and no speedometer, but it moves along nicely withy a couple of people.No trouble planing."
 

bglhooked

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i had an 1983 19' seaway with a 1991 60hp evinrude 2 stroke. It did 24knots wide open and went along at about 21 knots at 3/4 throttle. It was fine for everything I ever did. If i really loaded it up with 4 guys and some stuff it went along at about 18knots at 3/4 throttle. The problem you need to keep an eye on is the weight of the motor and the scupper height. I feel that that 60 hp was perfect for the boat. Motor was light enough and had plenty of power for me.
 

cjmahm

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Jangles, I have a 1987 Seaway 19 Cuddy Cabin which i bought a few years ago. When I bought it, it had the original 110 Johnson on it. When I went to repower a few years ago, I had some of the same reservations you are probably having about going to far one way or the other. I think you would be okay with the Honda by yourself, but loaded with gear and passengers might make it a bit sluggish. I opted for a 90 suzuki during our repower. The 70 probably would have been enough, but the weights were identical, so I went with the 90. We cruise comfortably at 15-20 mph, but can open it up to around 30+ if need be. Don't get the punch out of the hole an ETEC probably would, but works just fine. I have been very happy with it and the way she sips fuel. Good luck!
 

Jangles

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An update:

I rigged the BF50. Got the boat out this weekend, in light chop (1-2ft) with 2 people (320lbs) and 12gal of fuel with canvas down:

5800rpm made 21kts (24mph)
4500rpm made 16kts (18.5mph)

I didn't write down the prop dimensions, so I'll have to update this again. I think its an 11 5/8 by 11p but I can't remember. Hole shot was fine. Not neck breaking, but would plane in a few seconds. I have no need to go faster. Sea state will restrict speeds to around 15kts anyway. As it was, spray was getting heavy at full tilt.

Goal met, regardless. I wanted to make 20kts, and it does! Would I like to hang a 90 on it? Yea... probably. Not worth $$ right now though.
 

tomy

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have a 90 hp evenrude E-tec I bought new in 08,,,,nice fit on my 19 seaway...As I run a 36footer now, may be willing to sell motor seperate as I don't use much...Tommy
 

Spence

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FYI, the BF50 is a 4 stroke, as are all Hondas, in case you didn't know.

Also it seems the HP ratings of old 2 strokes (crank) do not equal modern ratings (prop). Supposedly the older 2s are up to 10% off on top of being measured at the crank, so that old 90 may have actually been putting out closer to 75 at the wheel. The new Honda would be a true 50. So 70% of 75hp is 52.5, perhaps close enough.

I'm trying to convince myself it's going to be good enough.... and it probably isn't.

My understanding is that Mercs HP were and are measured at the prop and most other brands at the crank hence a 10 hp Merc was always "stronger" than a 10 hp Johnson. I know that a few years ago when every motor line rebadged Tohatsu's 3.5 and sold it as their own that Mercury labeled their version the 3.3

I'm running a new 24' Seaway (hard chine) with a Yamaha 115 which weighs 2800 (boat only). She will do 33 mph with just my wife and I aboard and cruises at 20 mph at 4,000 rpm. She will do 25 mph with 7 passengers. My guess (and its no more than a guess) is that if you put a big diameter small pitch prop on your Honda 50 she would cruise comfortably at 15
 
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