top speed from a 40hp 2 stroke yamaha???

[NickJ]

I've just purchased 2001 yamaha 40hp 2 stroke with a stainless steel power tech prop, to replace 1992 28hp johnson for my 15.5 aluminum boat. Love the boat, however i found it was lacking in power with the 28hp on the back....
The boat is a 1992 sea nymph TX155 weight approx: 390lbs without the motor i'm assuming. Could anyone give me a ball park figure of what top speed i could expect with the newer 40hp yamaha on the back. Any info would be greatly appreciated.
Fantastic site BTW..

 

[Silvertip]

Re: top speed from a 40hp 2 stroke yamaha???

28 -- maybe 30 on a good day. But it all depends on state of tune, health of the engine, condition of the hull and load.

 

[mr 88]

Re: top speed from a 40hp 2 stroke yamaha???

33 to 36 mph. Depends on number of people. gear ,beam of boat,where controls are and if is trimmed out. Nothing in it, all weight including you towards the stern you might get a few more mph, just a guess.

 

[NickJ]

Re: top speed from a 40hp 2 stroke yamaha???

Thanks for the feedback, looking forward to getting the project underway, it has tilt and trim with remote. In terms of the beam of the boat i'm not sure.
I like the 33 to 36 mph...makes for a nice gain for sure.....it would a definite improvement to the roughly 20mph i was getting the 28hp...

 

[NickJ]

Re: top speed from a 40hp 2 stroke yamaha???

Thanks again for the feedback....
The boat is a 1992 sea nymph tx155 with console and controls..with a max rating of 35HP. Is there any real warm in replacing the current johnson 28hp(weight approx 130lbs) with the Yamaha used 40hp(weight approx 187lbs)?? Any info would be greatly appreciated
Nick

 

[99yam40]

Re: top speed from a 40hp 2 stroke yamaha???

Transom may not hold up to the extra load being put on it very well, but 5 hp is not that much extra.
here is a site to look at performance of different boat and motor combos. http://www.yamaha-motor.com/outboard/products/perfbull.aspx
It also tells what prop they were using. That will make a difference in the speed.
Just remember to make sure you have the proper prop for the load you run and be able to reach the proper WOT RPM

 

[NickJ]

Re: top speed from a 40hp 2 stroke yamaha???

Thank you for the reply, the transom looks quite solid, and able to accommodate the extra 60lbs. However, that being said, is there anything i could or should do to strenghen the transom ie: marine grade plywood? thanks in advance
Nick

 

[jakelogsdon]

Re: top speed from a 40hp 2 stroke yamaha???

You should be pushing close to 40 mph, it depends on the diameter and pitch of your prop and wot rpms. I don't think its too much motor for that boat, it will handle it.

 

[NickJ]

Re: top speed from a 40hp 2 stroke yamaha???

Thank you for the reply...those are some very nice in terms of speed improvements. I purchased the used yamaha 40hp a last week and had is shipped up here to Canada. I'm really looking forward to mounting in the early spring. It came with 704 controls and the whole package seems to be in very good shape.
I'm fairly mechanical and handy, however I've never rigged a larger outboard with trim/tilt. My question is was is exactly involved in mounting it?
ie:
1. Aligning the cavitation plate with the bottom of the boat?
2. running the cables and mounting the control?
3. Current 28hp Johnson has 2 bolts through the transom, should the 40hp have 4?
4. Is there any additional wiring involved besides connecting the positive/negative to the battery, i don't have any gauges on the console to wire in?
5. I haven't had a chance to power up the yamaha, once the battery is connected will the trim/tilt work? Or is addition wiring needed? Notice there are pigtails coming out of the side of the (704)controls...are they for accessories etc?
Unfortunately, don't have a garage otherwise the project would be underway. Any information would be greatly appreciated. Thanks
Nick

 

[madman2021]

Re: top speed from a 40hp 2 stroke yamaha???

the transom should hold it just fine. i had a 14 foot jon boat rated to hold 15hp. i had my 50 evinrude on it with a side console. i ran the boat like that for about 3 years. never had a problem with my transom. power was awsome. needed extra power due to all the weight i added. turned it into a mini bass tracker.