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skanperch

Transom motor weight ratio to boat size

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Hello to all in the forum......for 15 yrs I've owned a 16.5' Starcraft Camp Boat, with a 25 hp 2 stroke Merc. I'd like to get a new motor for this rig, a 4 stroke..... But every 25 hp 4 stroke I have looked at weighs 50 to 60 pounds more than my current motor, and I am questioning if that extra weight would be too much for the transom to bear. Also, I am wondering if that extra weight in the back affects the boat's handling. I have tried to contact Starcraft directly, but that has proven to be Mission Impossible, so I'd appreciate any experienced opinions/observations any of you might be able to share. Thank you .

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Like most everybody else, I had two strokes.  Then I finally upgraded to a 16.5' Alumacraft, tiller control with a 40 hp, EFI, 4 stroke Yamaha.  Best upgrade I ever made.  I've had no problems with the weight back there but, then again, I never ran a 2 stroke on that particular boat either.

I do like the 4 stroke though & would never go back to a 2 stroke.  The boat goes so fast that I don't even need to open it up all the way (goes ~28 mph, not wide open.)

Have you thought about (don't laugh) taking a 50# bag of potatoes with you, put it as far back as you can & make a test run?  Out of the hole will be different but you'll know what the extra weight feels like for steering & wave action.  Or take two AGM batteries on board (about 45# each) & give the extra weight a try.

The 4's are reliable, start on a dime & haven't had any problems.  The only issue is that they need to warm up otherwise they run like sh&t.  Do about 3-4 min warm-up. 

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If the transom is in good shape (not waterlogged or rotted), it strength should be enough hold the extra weight without a problem.  The problem most small boat have in repowering with a four stroke is that they were not designed for the extra weight resulting in really low freeboard at the transom and difficulty getting on plane.  I'm guessing your 25 weighs around 110 lbs.  A four stroke 25 will weigh as much as 170.  You could find yourself with only 2 to 3 inches of free board by the motor after you load the boat they way you would to use it. 

 

Check to Coast Guard capacity plate in the boat and see how much weight it can handle.

 

As suggested earlier, launch the boat and put some weight right in front of the motor, don't spread it across the stern. Two batteries is a good idea.  Run the boat and see how it sits in the water and how often you take water over the transom.  Move around and see if everything still feels good.   I rebuilt a 16' fiberglass skiff a few years ago, replaced a 25 HP 2 stroke with a 25 HP 4 stroke and found it was always taking water over the stern.  Sold the 4 stroke and bought a new 2 stroke to get the weight back down.  Your boat might be able to handle it but I would test it first.

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Not speaking from experience, but everything I have read is that the Etecs are lighter than 4 stroke, but still perform like one. I am sure someone will chime in to the good or the bad, but at least the conversation will be had. Just a thought.

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guffins...looking at E-Tecs is a good idea.  Never though of that.  I fish with one guy who has an E-Tec (70).  Never had a problem & we'll do a slow troll all day with no prob's.  Winterizing is different as you just go thru a sequence.  I heard there were problems when they first came out with high required fuel pressures but haven't heard anything lately.

I'll throw my extra weight (with the 4 stroke) up in the bow.  I keep the trolling motor battery, extra fuel tank, anchors & any other weight up there.  It helps to keep the boat even.

Edited by Smeltz

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Smallboat's dead on IMO. That Coast Guard capacity plate will tell you exactly how much weight, as well as maximum horse power  your boat is rated for. Checking Starcraft's website, I see they have a 16.5 tin rated for 1100 lbs, not sure if your boat is similar but it wouldn't surprise me, if the boat is structurally sound. I have an 18' tin and it's rated for 1650 lbs with a 150 hp max. I worry about freeboard as well and am considering White Cap splash guards

 

http://www.whitecapmfg.com/

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The newer boats for the four strokes have a wider beam and transom to support the heavier engines. moving your battery forward could help. Taking a swell over the stern could sink your boat in seconds so keep your stability safe. Be careful choosing a heavier motor than the boat is designed for.

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[PDF]safety standards for backyard boat builders - New ...
newboatbuilders.com/docs/backyardboatbuilders.pdf

U.S. Department of Transportation. United States Coast Guard. SAFETY.

This PDF has some good hints as to what HP goes with what boats.

 But to give you an idea of weight. A 1990 2stroke 25 horse Johnson is 115 pounds and a 2015 4stroke 25 horse tohatsu is 157 pounds.

I would not worry overly much about the extra 42 pounds. Moving your battery to the front of the boat will solve your problem. Moving your gas tank is less advisable  because as it empties out it will change the balance. So the best place is in the back.

Edited by rolmops

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Thanks to all who responded. The freeboard matter is one I'd not given any thought to.....so yes, I will try to put a 50 lb battery next to the transom to see how it affects clearance.

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With today's 2 strokers, oil injected just add gas, keep oil reservoir capped off, they are quiet from what you got now. Maybe even a little lighter?? My uncle put a new 2 stroker on his aluminum 16.5, mister muskie, I know that's the make but I'm not sure of the manufacturer. It had a 60hp. Chrysler I know that's not much to come pair to, but we were amazed with its performance, and the dealer told Dave, and he could drop to a 50hp. I would look into the 2 strokers just for shyts and giggles, unless your dead set on a 4 stroker. Don't get me wrong they both pro's and con's but I'm really impressed with his new Merc. I will say he can't troll with it, it's speed at an idle in gear is 3 plus other then that that's the only down, he runs 2 of the smallest socks the Amish outfitter sells, actually a little throttle to get 1.5-1.8 That's the only down fall I sea. Good luck which ever direction you choose!!

Edited by pap

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Thanks to all who responded. The freeboard matter is one I'd not given any thought to.....so yes, I will try to put a 50 lb battery next to the transom to see how it affects clearance.

You would need to put it on top of the motor to get the correct weight hanging off the transom.

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