New mercury 40hp

[Johnsk]

So I changed out my 25 hp Mercury four stroke which got 23 miles an hour wide open to a 40 hp Mercury four stroke got 35 today with myself and another guy two batteries one upfront when both of us sat in the back at wide-open I would start to get some porpoising if he sat upfront we didn’t get it but he didn’t like sitting up thereAny recommendations

 

[1960 yellowboat]

yeah
slow down
or change the tilt on the motor and slow down

 

[GYPSY400]

If its porpoising the trim is too high.

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[Weldorthemagnificent]

Trim down or put more weight up front. Fuel tank, cooler full of fish....

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[Johnsk]

Thanks , it has PT when I trim down The porpoising goes away it just seems like the bow is not up high enough when I’m running, if I cruise around 28,29 run fine guess just don’t run WOT just had to see after running so slow with 25hp.

 

[MrGiggles]

Thanks , it has PT when I trim down The porpoising goes away it just seems like the bow is not up high enough when I’m running, if I cruise around 28,29 run fine guess just don’t run WOT just had to see after running so slow with 25hp.

Probably a side affect of the much heavier outboard.

You can either move some weight up front, or try a hydrofoil. A 4 blade prop may help as well.

 

[Johnsk]

Yeah I’m thinking about putting the second battery upfront also it weighs 65 pounds that might help move some of the weight forward and have less weight in the back

 

[LDUBS]

I experienced a similar mph "upgrade". But not from swapping out motors. I went from a 15' 25 HP boat to an 18' 50 HP boat. MPH gain was similar to yours. I went from about 25 MPH tops to 32 mph on the new boat.

To me gaining that extra 10 mph is pretty satisfying. Cruising along at 28/29 mph at less than WOT is good too!

 

[1960 yellowboat]

Do you want to fish or water ski?
What's the big attraction to going fast?
Down here, the recommended HP rating on a boat means nothing.
14 ft jon's with 35 to 45 hp motors on the are all too common
Slow down and enjoy the ride

 

[LDUBS]

Do you want to fish or water ski?
What's the big attraction to going fast?
Down here, the recommended HP rating on a boat means nothing.
14 ft jon's with 35 to 45 hp motors on the are all too common
Slow down and enjoy the ride

I'm pretty happy cruising to my fishing spots at 28/29 mph. That isn't exactly racing speeds. Not sure the purpose of your post.

 

[Sinkingfast]

Well...for me I need some hustle when the clouds move in. I rarely move over 15mph and usually slower most of the time but storms are hard to see where I am and have only 15min or so to get to port.

On my 1236 with a modded 15hp I use a 4 blade with a homemade plate like the paratrim. Works like a dream.

 

[LDUBS]

Running from weather is a good reason for some extra speed. Not near as critical but sometimes I have a long run to where I want to fish. Nice to be able to get there comfortably without having to wind the motor up. I can always slow down if conditions warrant.

 

[turbotodd]

What you are describing is perfectly normal assuming there's nothing wrong with the hull (rocker). That is exactly what trim is for. When you load the bow, you can trim up. When you load the stern, you trim in.

The 40 is a little heavier than the 25 and that doesn't help.

A prop with a lot of rake tends to "lift the bow", and on a lot of aluminum hulls, can cause porpoising. You can switch to a prop that has less rake.

Some setups will porpoise at part throttle and then you can power through it; but not all of 'em. Even some of the exact same models will exhibit stupid stuff like this because aluminum boats are rarely all identical. Thats just the way it is.

Sometimes the motor mounted too low can cause it too. Sometimes but less commonly mounted too high can cause it.

If all else fails, you can knock a hook into the last few foot of hull. Sounds brash but it's not uncommon.

 

[Johnsk]

Thanks for the replies , as far as slow down I’m mainly fish susquehanna River who wants to travel 5-10 miles at 18mph when u can go 28/30 get there in half the time more time to catch fish. I’m gonna more the 2nd battery up front and install a aluminum side box so my fishing partner can sit in middle on side of boat rather than on the back with me that should solve the issues. The boat is rated for 40hp tiller or 50 console. The 40 weights 40 pounds more than the 25hp. So move the 2nd battery 65lbs up front will help thanks. I’m gonna have my fishing buddy go on diet the winter also lol

 

[onthewater102]

Do you want to fish or water ski?
What's the big attraction to going fast?
Down here, the recommended HP rating on a boat means nothing.
14 ft jon's with 35 to 45 hp motors on the are all too common
Slow down and enjoy the ride

:evil: I'm sorry - where in his post does he even mention the size boat he's using the motor on - only the speed before and after the change. You make a lot of assumptions and pass an awful lot of judgement for a person working with no information beyond the simple fact that he went faster.

Thanks for the replies , as far as slow down I’m mainly fish susquehanna River who wants to travel 5-10 miles at 18mph when u can go 28/30 get there in half the time more time to catch fish. I’m gonna more the 2nd battery up front and install a aluminum side box so my fishing partner can sit in middle on side of boat rather than on the back with me that should solve the issues. The boat is rated for 40hp tiller or 50 console. The 40 weights 40 pounds more than the 25hp. So move the 2nd battery 65lbs up front will help thanks. I’m gonna have my fishing buddy go on diet the winter also lol

Wow - look at that - the setup ISN'T overpowered after all, there is a REASONABLE reason to want to go faster (cover a lot of distance in a reasonable amount of time) and if you knew ANYTHING about boats you'd know there isn't a SINGLE 14' out there rated for a 40hp tiller or 50 console - so clearly this guy isn't the person with the 14' who put your nose out of joint.

 

[turbotodd]

y'all outta come out to stuttgart and watch the duck hunters.

15' boats with 70, 80, 90hp outboards, almost all tiller steered. They spend more on the motors than I did on both of my cars combined! Mods?? Mod a 70 to make 130hp...seen it quite a few times and they scream. But for me, 30mph is fine (25hp). There's only been twice (that I can think of) I needed to go faster and once was in a boat race with a guy who had exactly the same boat with a 40. The other, outrunning the weather. We still got drenched but it was mid summer and before the shower, about 105° actual air temp so the rain felt nice.

 

[Weldorthemagnificent]

Special kind of crazy in Arkansas. I've seen some of that over by crosset on the oachita.

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[nccatfisher]

I have the same boat and it wanted to porpoise bad when my motor set in the stock position. I added tilt and trim and it was aftermarket thus it has a 5” back set and it stopped it.

But I also have two batteries up under the front deck and made a fuel tank that goes all the way across behind it that holds 10 gallons.

 

[Johnsk]

It s 2018 1648 grizzly till bought it with 25hp it was a dog cruise was 17ish I have 2 Amy batteries 1 in stern and one in how 2 guys and gear 460 and the boat weighs 590 max hp for boat is 40hp so that’s what I upgraded too. Much happier with performance can cruise 26-27 mph 4800 rpm I will be moving second battery to the bow , battery weighs 65lbs so that a little more than the 40 lbs diff in the 25-40 hp Merc thanks for replies.

 

[CedarRiverScooter]

It is just plain fun to skim along at 30+mph on smooth narrow river - Don't need any other justification!