Proper motor to boat question

[Trophymuskie]

I asked a while back about props as I was having not so hot top end on my 182 Ultima with a 115HP Honda. After reading many post about props I did some checking today to see my motor is set into the top hole and therefore lowest it can be. Now I lowered the motor almost all the way down as it hits the ground and noticed that my stableliser ( first plate above the prop ) is still a few inches above the bottom of the deep V of my boat. Can this be my problem? Did my dealer install a motor to short for my boat? I am getting but 37 MPH at 5600 RPMs with a 15 pitch prop with the motor trimed all the way up. I do get a great holeshot with a couple of people as well.

Catch a big one this fall
Keep releasing them all
Richard Collin
http://www.trophymuskiecharters.com

[Water Dog]

Except for notched sterns , the plate above the prop should be in the(clean water)flow near the same level as your lowest point behind the transom . Anything else is asking for problems and poor performance .
A 115 HP on your hull can do much better than 37 mph .
On our racing boats we use jack plates to adjust the motor height and set back . The props we use are made to spin in this thinner water flow .
A V bottem fishing boat has a different mission and design .
Talk to the boat manufacturer for proper set up .
Good Luck

[Trophymuskie]

Is this motor instaled the wrong one?

Catch a big one this fall
Keep releasing them all
Richard Collin
http://www.trophymuskiecharters.com

[Dodge1]

I really don't think you have a problem with the mounting of the motor or the shaft length. Since your saying that your hole-shot is good, that only reinforces my thoughts that your motor is mounted properly and it has the correct shaft length for your boat.

The real question is where your prop is, in relation to the bottom of your hull, when the motor is full trimmed down? The really go fast boats are tuned so that only the bottom of the prop is in the water, at full throttle, but that’s not the ideal situation for our needs.

I couldn’t find the transom depth for your boat but you might want to measure it and let us know how deep it is. That’s an almost sure fired answer to your question of right or wrong motor.

Honda rates the 115 at a max RPM of 6000. As a general rule of thumb, motors perform at their best when they run towards the top end of the allowable RPM range. When you say your pulling 5600 RMP is that with a couple of other people on board, a full load of gas, all your gear, or just yourself?

[Trophymuskie]

Sorry it took me so long but was out fishing the last few days of our season.

I measured the transom and it is 21 inches in the middle of where the motor is mounted.

As for 5600 RPM that is with almost full tank of gas and another angler as well as a lot of gear as I am a muskienut. I am sure it will go to 5700 or even 5800 when I am alone and a smaller load. But I am lucky to get 38 MPH GPS speed.

Catch a big one this fall
Keep releasing them all
Richard Collin
http://www.trophymuskiecharters.com

[Zamboni]

The grammer on this board is terrible.

[Mike1410]

Do you know what the gear ratio is in the lower unit on your Honda?

[Dodge1]

Richard,

Since your Honda has a 20” shaft and your transom is 21”, IMO you have the right shaft length.

My Skeeter 135 also has a 21” transom and my Mercury 125 has a 20” shaft. That puts my stabilizer about 1-½ inches above the bottom of the pad, so it’s probably very close to where yours is. My rig will hit just a tad over 46mph, with a full load and I mean full. So I think you might be having a problem with the prop you’re currently running.

You said your prop was 15” but is it SS or aluminum and how many blades does it have? I would call your dealer and ask what prop they would recommend in order to get your motor running at 6000 RPM, with your normal load.

[Rapaleye]

Richard,
I am by no means an expert on motors and props but I do pay a lot of attention to what the folks on this board say about them. If you conclude you have the right shaft length, it sounds like you are doing the best you can with that pitch prop. I went to the prop calculator page that a lot of guys on this board recommend. (try going to - http://www.rbbi.com/folders/prop/propcalc.htm). I went to Honda's page and it list your motor as having a 2.0:1 lower unit gear ratio. If you enter your 5800rpm, 15 pitch, 2.0 gear ratio, and a 10% slip it says you should go about 37mph and you are. If you then enter 17 pitch it says you should jump to 42 mph if you can maintain 5800 rpm. Even if you loose 200 rpm you should get to around 40mph. It looks like you just need to work with your prop pitch and mounting hole.
Good luck.
Jim

[Trophymuskie]

How many languages do you speak and write?

English is my second and was learned in the streets.

Je suis francophone de naisance.

Catch a big one this fall
Keep releasing them all
Richard Collin
http://www.trophymuskiecharters.com

[Trophymuskie]

I will try it out with the original prop I got with the boat as it was a 17 but if I can remember I could barely get 5400 RPMs with it. The only problem is that prop is a mercury and needs the center peace to fit my Honda motor. Had a lot of trouble finding one a few months ago till I finaly found one guy within 100 miles of here with a Honda prop.

If that doesn't work I will go out and buy a 13 inch SS prop to get to 6000 RPMs and therefore top speed.

Catch a big one this fall
Keep releasing them all
Richard Collin
http://www.trophymuskiecharters.com

[Mike1410]

What Rapaleye says is exactly where I was heading with the question about your lower unit gear ratio. I think that you are probably getting the performance from your rig that as you have it loaded you should expect. I don't think that there is a basic setup problem. One thing you mentioned was that to get your best speed you had to trim the motor all the way up. If that is correct, I believe that if you will move as much weight as possible to the back of the boat you will get the extra rpms and speed you are looking for.

[BlackSilver]

If you go to a 13' pitch, your RPMs will rise (as you expect) but your top speed will drop.

Hans

[Rapaleye]

Richard,
In my estimate I would say that you would want to find atleast a 17 pitch prop that is designed to go with your engine. I would try calling Honda directly and see what prop brands they recommend. At least find out what diameter prop and then work with a reputable prop shop to find that diameter and 17 pitch that will fit your engine properly. Then I would concentrate on how to get that prop to perform in the target RPM range, in this case probably atleast 5400 and better yet 55-5700. Try things like raising the engine a hole and moving the weight around in the boat. If that doesn't work keep asking the guys on this board for ideas. I am sure you can figure it out.
Good luck

[Dodge1]

Richard,

Prop selection really is a black art but these two sites can at least get you pointed in the right direction.

I use them both because the Mercury prop selector let’s you input your boats weight or length, your desired goal (handling, speed, hole-shot or?) and then provides you with several props that meet the parameters you input.

Weight, and where it's placed, really has a major impact on your boats performance. However, most people grossly underestimate what their fully rigged boat really weighs. Find your boats dry weight, add the weight of the motor, fuel, fishing gear, people on board (don't forget yourself) and then add at least 250lbs (more if you run with the livewell full). You could take it to a truck scale with all your gear on board but then you have to subtract the weight of the trailer, add the weight of the people you normally carry etc.

http://www.rbbi.com/folders/prop/propcalc.htm

http://www.mercurymarine.com/cgi-bin/mercprod/MercuryHome/Templates/DotComTemplate.jsp?page_id=317&BV_UseBVCookie=no&BV_SessionID=@@@@0425238083.1007378179@@@@&BV_EngineID=ddadccjgkdedibeecfececjg.0

By playing with the variables on these two sites you can come up with a very good idea of what prop and pitch will provide the results you’re after.

BTW – everyone seems to be obsessed with top speed but I run a Merc High Five because of the handling advantages it offers. I also found a couple of sites that suggested that if you’re going from a Merc 3 blade SS, to the High Five, you could keep your current pitch or maybe even move up one inch. Now that was exactly opposite of what the Mercury site suggested and what everyone was saying on this site but their advice proved to be correct, at least in my case.