Prop Pitch Recommendations/ideas Please
 

Hi Guys.

Looking for some advice. I have a 14 foot Lowe Fishing model aluminum boat with a 25hp mercury on the back. The boat weighs 601lbs without the motor which is 148lbs and the safety plaque says 5 people or 550lbs for gear and people.

I am about 205lbs, battery is 65lbs 6 gallon fuel jug, fishing gear, and then my fishing partner (my daughter) is 125 lbs. so with the motor we are basically capacity. When my daughter takes the boat out lets just say it moves a little faster without me on it and planes a little better, but I do not think it gets out of the water as much as it should. When just me on the boat i have to stand to get it to plane out somewhat and move a little faster, and when I turn slows down and bow up again, when both on the boat i have to sit up the bow but we are still throwing a wake more than it should
all of the above is at WOT. In all conditions (except with just my daughter on the boat, and even then in watching it does seem like still could see a little help), it just seems like it should be a little more out of the water and then obviously move quicker than it is. add this one: don't even think about touching the trim slows it makes it sit down even more. The engine is in perfect running condition and has been combed over.

The engine and set up from boat maker and mercury calls for a 9 inch pitch to and 11 pitch but we all know they are guidelines for the most part and it has to be application specific. It is a 10 spline prop shaft. Currently there is a 9.9 x 9 pitch on the motor (brand new) and I have put a foil on (SE200) to help it get up out of the water, it helped a little but it seems like the motor is working hard and the boat itself is weighing it down so to speak.
I have pulled as much weight as I can out of the boat already, understand more pitch is more speed but slower hole shot. So do i increase pitch and diameter as well??? How do I test everything out without buying numerous props and being stuck with them?

I have a 10inch x 11 pitch stainless prop to put on there, but mechanic advised not to use it due to the weight of the prop and the size of the motor and the lower end and shaft taking the extra weight on??

help me out here. thank you

You could try using this prop sizing calculator, worked perfectly for my Pontoon Barge. Just make sure your not over revving the motor at WOT

https://www.miwheel.com/outboard-pro...zing-analysis/

Or my favorite - bolt more power on the back

I wish on the power end :emb:, but she is not of license age yet (1.5 years away).

I have used some of those selector sites and they show 9-11 pitch. on the link you provided (thank you very much) it shows 10.5-12. it seems its all over the place.

I have read that that lower-horsepower engines can bog down if fitted with an outboard propeller with too high a pitch and diameter, and that can wear heavily on internal engine parts.

The first thing to do is to determine your WOT rpm at the typical loading you run.

You want your prop to give you at least the lower number of the rpm range with a full load.

The boat will operate better with the rpm at the top of the range but you must be careful not to over rev it when lightly loaded.

Once you know where you are you can figure out what prop changes to make.

The difficult part with all this is getting accurate rpm readings.

For this you need an appropriate tach.

I bought this timing light for my two stroke outboards and it has a tachometer on it:

INNOVA 5568 Pro-Timing Light with Tool Case https://www.amazon.com/dp/B000EVU8J8..._bNPWEb6AYWHTG

I didn't notice a mention of the motor being a two stroke or four stroke but it works on both.

If it is a two stroke you might also want to try this product:

Quicksilver 858080Q03 Power Tune Internal Engine Cleaner, 12oz - for 2-Stroke, 4-Stroke and Fuel-Injected Gas Engines https://www.amazon.com/dp/B000XBFL0K..._AJPWEbTV4VARR

It clears out build up in the exhaust and lets your motor breath better.

PM sent...

If your worried about a non-licensed under age operator isn't a 14' boat too long anyway? FYI - I don't really keep up on that, all my kids are licensed.

it is a 4 stroke EFI

as long as boat motor is 25hp or less, license not needed, has nothing to due with length of boat

Speed test done with phone speedometer gps app and just daughter on boat
Max speeds at WOT
solid 18mph in one direction 3 times same distance
and 16.5/17 sometimes hitting 18 in the other direction 3 times same distance

thoughts?

Max speed at WOT, gearing and 6000rpm is 24mph for this motor

Just like a car and gears. Too much prop and it will bog, not enough and it will over-rev. The key is finding the sweet spot. A lot on marinas have used props that they may let you try.

thank you I will make some calls, I'm ok with the hole shot not being spectacular but speed and getting the hull out of the water is more what I am looking for at this point. again I do have a foil on the motor.

I think you're just asking too much out of that motor for that much weight. I would consider more power.

If it's not planing cleanly and seems to be straining, you need less pitch. Try an 8" pitch. The 10" pitch SS prop you have will not help at all.

The experiments will begin Friday lol. In having looked at the motor placement further through suggestions, the anti- ventilation plate seems to be 2 inches or so under the keel line of the boat, which is a big no no. Old owner i know took the motor off at one point and probably installed it too low.

So step one is to move the engine up, which I have room on the bracket to adjust. Then I will by doing runs with the props to see performance results. with a tach tester.

With a boat that small it's not so much the prop pitch as it is the weight distribution. As you describe just shifting your self a couple or more feet forward makes a huge difference in how well the boat gets up on plane. If you have all the weight in the back of the boat already you are at a big disadvantage as you're asking a lot of the motor to have the power to push that up on plane with nothing to push the front down. I do not think that a different pitched prop will help much as you may hope it does. Those foils you put on the motor never seem to do much if anything at all. Ultimately you need to get more weight in the nose of the boat or get more motor. Just my thoughts.

I had a 14 foot boat (side console) with a 30HP on the back. It performed well with up to three adults in the boat BUT me as the driver was sitting mid way up the boat, passenger #1 seat was to the left and slightly forward of the captains seat, third adult was fine on the back seat. I did pitch down but that did not make a huge difference, some but not huge.

the console is midship which is good. I'm hoping just picking the motor up as it is being dragged down by the water going above the anti-vent plate will start the change. Has to be a reason why Merc, Lowe and all the prop website are saying 10/11 pitch sizes mostly

the boat can only go up to a 30hp motor and the boat is rated for 5 people or 550lbs ontop of the 601 lbs the hull is. With that in mind i do not see 25hp being underrated for this boat, and I know the motor is running the way it should.

let's see what happens

I'd take that plate off and see what difference that makes. One thing you want to be careful of is not to raise that motor to much and cause a cavitation problem once you're up on plane.

I don't have my 14 footer anymore but I seem to recall I put an 11 pitch on it which was as low as I could go for that motor. That replaced the 13 pitch that was on it.

Ya know you might want to try a 4 blade spitfire prop on that motor if they make one. Gives a ton more bite and helps with the hole shot for sure.

If you can't really go with a bigger motor than I would assume that your package is optimized as best as it can be and agree it should be sufficient to handle what is on the recommended person\weight plate.

Once I move the motor up, I am going test out a stainless 11 pitch I have and I also have a spitfire 4 blade with an 11 pitch that was supposed on there before I did the lower end over from the old owner. It is a little beat up so I did not want to put it on, but i am going to use it in the test runs, as well as the current 9 on there now

Good luck, nice thing is you have some options to test.

anyone have any 3M 4200 lying around? wanted to seal around the bolts once finalized for location (5200 is permanent). buying a $20-25 tube to use about 1/20th of it seems crazy to me

Amazon has it cheaper...


3M Marine Adhesive Sealant Fast Cure 4200 (05260) – Semi-Permanent Flexible Adhesive Sealant for Boats and Marine Applications – White – 3 Ounces

https://www.amazon.com/dp/B0000AY6B0..._ABDXEbQX311W5

I doubt raising the engine is going to make a big difference. Adjustments to the X dimension are more of a top speed fix than a "getting it to plane" fix, but you should get that adjusted properly regardless. I hope I'm wrong about it not helping much.

Fully agree but wont get by tomorrow unfortunately, even when i looked yesterday or Tuesday.

Now just realized that needs up to 24 hours to cure, looking for a faster cure product now

in speaking to 2 different prop companies I have been told allowing water over the top of the anti vent plate from the back of the boat actually pushes down on the motor and prop and creates a very large drag situation. Fixing this they said will/should be a drastic change, again they said lol

right now the anti vent plate is below the keel while just sitting in the water and no added weight to the boat nor underway, then when getting on it and underway I am just dropping it lower under the water line.

hoping they are right

At WOT and when boat is up on plane, you should be able to see the anti vent plate right on top or just into the water spray. If you cant see it you need to raise the motor which will create a lot less drag.

I think your on the right track...

Good Luck!

Dan

Update:
Well upon measuring the motor was 3 inches give or take below where it should have been. I moved it up ad far as I could and still could go a touch higher but need to get it out of the water to do so. Got it up almost two inches. Significant difference and it ran better with the 9 pitch than the two different 11s, speeds into low 20s and easy plane. I am going to get a 8 and run a test from there