what should a new 15hp 4 stroke do on a 1436 jon ?

[back4more]

thanks again for the input everyone.

sorry for not answering this earlier ...

DrNip » 28 Feb 2014, 09:11[/url]"]Looks like you asking a whole lot out of that 1436 and 15 HP with 3 people and all the excess weight. Was the 3 people just a test for the engine or are you actually out fishing with 3?

my wife, daughter and I were just out cruising, something we plan to do a lot.

also, the 15hp does have a doel-fin stabalizer. Ive had a couple jon boats before with 9.8-9.9's and they were difficult when I would go out alone.

 

[DrNip]

Well I would think that you could get at least 5-7 more mph of it with the 15 hp.

 

[back4more]

DrNip » 11 minutes ago[/url]"]Well I would think that you could get at least 5-7 more mph of it with the 15 hp.

sorry if I wasnt clear, the 17mph was with the doel-fin installed on the 15hp.

 

[scoobeb]

bcbouy » Yesterday, 09:52[/url]"]fftopic: the op doesn't have a 20 hp.why do you keep comparing a 20 to a 15? 5 hp is 25% more power.put a 20 on an 18 ft. boat then compare.

I was commenting on turbotodds post with his friend having a 20hp tohatsu.Plus he asked what prop pitch i was running,Did you miss that post?Also i only talk about a 15hp through out this whole thread besides what question i answered again from turbotodds post,that's it.

The only thing i said was that the 15/20hp merc or tohatsu was the same engine except for i believe the carb is jetted different.

Just for more info,tohatsu makes,of course tohatsu,nissan,and mercs up to 30hp,they also make all,yes all or evinrudes 4strokes up to 15hp,all they are is tohatsu's with evinrude stickers on it and they sell them for hundreds more like the mercs and nissans.That's why i get a kick out of people who say the merc is way better then a tohatsu or nissan when tohatsu makes their motors up to 30hp.A lot of people don't know these facts.

The difference in speed between a 15hp and 20hp is very minimal,a few mph at best.Even though it's a 25% increase in power,that's really what the 20 will give you over the 15,more torque when more weight is in the boat that the 15 will struggle with to get you on plane.You will be able to get on plane with the 20 way easier then the 15,but as far as overall wot it's a very minimal gain at best.

 

[Rat]

bcbouy » 01 Mar 2014, 17:39[/url]"]

scoobeb » Today, 13:37[/url]"]That boat should fly even with that weight in it.I have a 1436 with a 20hp and it does near 30mph with me and near 28mph with 2 but with 3 it would probably be near 23-25mph.The 15merc/tohatsu(same motor) has a ton of power and you should do near 20-23mph with no problem.

i respectfully gotta call bs on that. theres no way a 15 horse can get those speeds with #550 weight.especially a john.my 9.9 didn't get those speeds pushing a 120 pound 12 footer.

My 12 footer with a 9.9 4 stroke would run 26 mph all day long with me and gear. With an extra person and gear she would run 20 MPH.
The RatKraft, 14 footer decked out, with a 20 HP will run 24 MPH and 20 MPH with an extra person.

You could have several problems:
1) As stated above, incorrect pitch will have a huge effect; heavy boat go heavy on pitch.
2) Make sure you are hitting the RPMs for the motor, again this is pitch
3) Make sure the motor isn't too far below the chine, the ventilation plate should be even or just above the bottom of the boat for best performance.
4) Do you have a Dol-fin (or similar) on the motor? If so, it should be out of the water when on plane.

I don't know what you should be getting but you should see a better increase than 4-5 MPH from a 9.9 to a 15 HP; unless the 9.9 was some kinda wicked good motor.

 

[back4more]

Rat » Today, 11:49[/url]"]

My 12 footer with a 9.9 4 stroke would run 26 mph all day long with me and gear. With an extra person and gear she would run 20 MPH.
The RatKraft, 14 footer decked out, with a 20 HP will run 24 MPH and 20 MPH with an extra person.

You could have several problems:
1) As stated above, incorrect pitch will have a huge effect; heavy boat go heavy on pitch.
sorry for such a noob question, but you mean whats referred to in the motor manual as the trim angle ?
2) Make sure you are hitting the RPMs for the motor, again this is pitch
will work on this after pitch is determined
3) Make sure the motor isn't too far below the chine, the ventilation plate should be even or just above the bottom of the boat for best performance.
my ventilation plate is really close to even with bottom of boat, checked it with a level last night
4) Do you have a Dol-fin (or similar) on the motor? If so, it should be out of the water when on plane.
I do have a doel-fin installed. I will check next time Im out to see if its out of the water on plane

I don't know what you should be getting but you should see a better increase than 4-5 MPH from a 9.9 to a 15 HP; unless the 9.9 was some kinda wicked good motor.

my 4 mph increase is going from a 6hp to 15hp

 

[Rat]

back4more » Today, 17:57[/url]"]

Rat » Today, 11:49[/url]"]

My 12 footer with a 9.9 4 stroke would run 26 mph all day long with me and gear. With an extra person and gear she would run 20 MPH.
The RatKraft, 14 footer decked out, with a 20 HP will run 24 MPH and 20 MPH with an extra person.

You could have several problems:
1) As stated above, incorrect pitch will have a huge effect; heavy boat go heavy on pitch.
sorry for such a noob question, but you mean whats referred to in the motor manual as the trim angle ?
2) Make sure you are hitting the RPMs for the motor, again this is pitch
will work on this after pitch is determined
3) Make sure the motor isn't too far below the chine, the ventilation plate should be even or just above the bottom of the boat for best performance.
my ventilation plate is really close to even with bottom of boat, checked it with a level last night
4) Do you have a Dol-fin (or similar) on the motor? If so, it should be out of the water when on plane.
I do have a doel-fin installed. I will check next time Im out to see if its out of the water on plane

I don't know what you should be getting but you should see a better increase than 4-5 MPH from a 9.9 to a 15 HP; unless the 9.9 was some kinda wicked good motor.

my 4 mph increase is going from a 6hp to 15hp

1) & 2) Pitch refers to the pitch of the propeller not the tilt or trim of the motor. A boat only has one forward gear so imagine that the one gear was equivalent to 1st gear in a truck; this would be great for a truck that always pulled heavy loads but not good for one that wanted to go fast or pulled light loads. Now imagine if the truck only had third gear; you could get much more speed than the one with only 1st gear, but you could not pull a heavy load. This is what prop pitch is doing, changing the gear ratio.
Read this article: https://www.comprop.com/pickprop.html

Getting the most out of your motor is all about getting the right pitch (gear) for the boat; and how we do that is by using the engine max RPM at WOT. You will need a tachometer like this, https://www.tinytach.com/. It doesn't need to be mounted or anything you can just hold it in your hand for the test; it is good to have a tachometer though so I recommend mounting it in the boat.

A) Look at the prop you have now, there will two numbers stamped on it; the first is the diameter and the second is the pitch. As a rule you will keep the same diameter (within 1/2 inch anyway) but change the pitch to tune the drive.
B) Hook up the tachometer
C) Load the boat with what it will normally be carrying
D) Run the boat at WOT and make note of the RPM and speed
If the test shows you are not making it to max RPM you need a lower pitch (down shifting) and visa versa. Each inch in prop pitch will make about 150-200 RPM difference.

Some recommend removing the Dol-Fin for the tests but I haven't seen any interference when I have done this type of tune by leaving it on. Just make sure that it is out, or mostly out, of the water when on plane.
If not you need to raise the motor to get it out of the water when on plane. I use 1/2" battens and paint stirring sticks to fine tune the height on the water.
A) I raise the motor 1/4" at a time until the motor starts to ventilate in tight turns, then back it down 1/4"
B) Later you can build a permanent shim for the top of the transom or add a jack plate
C) There is a great tutorial for a DIY Jackplate here: Homemade Jackplate
You may end up with the ventilation plate higher than the bottom of your boat, that's okay. Tuning the height will ensure the motor is at the right depth so there is minimal drag but it is low enough that you don't ventilate and over-rev the motor in turns. This should be done before the prop tuning. All of mine end up above the bottom of the boat somewhere between 1 to 2-1/2 inches usually.

Once you know the right prop pitch you can keep a lighter pitch in the boat as a back up and you can swap them out easily for when you are running light. I kept a light pitch on my motor because I usually ran light and my back up prop was heavier for those times I was going camping and had heavy loads. I am hard on props, so I always had a spare for those time I broke a blade or spun the hub. Keep a wrench, cotter pins and an extra castle nut in the boat as well; eventually you WILL drop one of these over board and it's nice to have a spare!

 

[back4more]

thank you very much for the detailed information Rat. Im going to stay away from buying a new prop right now, but will revisit the idea in the future. Ive already bolted the motor to the transom but may go for the jack plate, if needed. that homemade plate looks nice.

 

[scoobeb]

Be careful with using the dolphin,even know it's unlikely the cavitation plate can snap.Those dolphins do put as lot of pressure on the cavitation plates.Like i said it doesn't happen very much at all but it could.I have never used one and never will.I will do everything in my power to get the motor mounted right or change props before i do that,if that won't work i will sell the motor and buy a 2stroke.I have never had those issues of power loss though.Every boat i have ever had the motor sits around 1 inch below the bottom of the boat or dead even and has ran like a rapped ape.Weight distributed the wrong way is the only issue i have ever had.A dif prop can do wonders though in certain applications if needed.

Good luck.

 

[back4more]

thanks skebob, I may try it without the doel-phin next weekend.

I took it out today and found out a few things.

first of the way I used a app on my phone (GPS Essentials) to determine that the 6hp pushed my empty boat and me 17mph. when I took out the 15hp motor, with wife daughter and I, I got my 17mph speed from my lowrance mark 4 ff/gps combo. today I found out that the two devices have a variance of as much as 2-3 mph.

when I went out alone I reached 20.0 based on the lowrance, and something like 22.9 using the phone app. I went back to the dock and changed my trim angle from the 3rd hole closest to the boat, to the 2nd hole closest to the boat. not good. I didnt even let the motor top out. the front was plowing water. went back to the dock and changed the trim angle to the 4th hole closest to the boat (as shown in pic below). this was much better, got me up to 23.3 mph. added the wife and daughter and we did 19.4 (compared to 17.3 or so last time)