please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinrude)

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Oh, and a friend mentioned that maybe I needed to run half a can or so of sea-foam through the carb to help get it all ungunked after sitting. thoughts on that maybe it is an "22 year old engine" issue that's been sitting a lot for the last 2 years and a lot of years before that? I did rebuild the carb and replace the water pump and thermostat when I got the boat about 3 years ago, but it has sat quite a bit in the last year and a half.

Thanks.

 

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Can your budget handle $77.99 for a Solas Amita 10 X 7, 4 bade prop?

probably. May cost that much to get the shop to "tweek" this one more as it is - not sure if but I think I remember they do hourly work for these types of mods (like to take off 1" of pitch as was suggested)...
Is 4 bladed better? I thought they would make it work even harder...? Maybe I remember it all backwards. I need to start doing some re-research on this whole thing now that boat should be getting used more again.

 

[dazk14]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

1st- That's way to much reading. Your engine isn't developing full power at 5000 rpm. It needs to run up to 6250 to get all 15hp. You're probably getting ~12 at 5000.

As I recall, the full throttle RPM range is 5500-7000, so it needs to rev to get it's full power. That's good news for you.

Get a price to remove some pitch from that prop. Leave the cup. an 1" decrease in pitch will gain quite a bit of rpm's, but I need to see some data. Ask them if the prop now has single or double cupping, although that's not an exact numerical term.

Post a grid of approximate weight, speed, and rpm.

Do you have any "before cupping" speed, rpm, load data.

Properly setup, that 15 should be suitable for your needs. We just need to get all the power to water. Those are very nice motors, with tons of used parts available and very good resale value. Up to $750 for a nice one.

Edit: a more accurate word than "suitable", is probably "functional", but again there was so much written, let's see the Cliff Notes version.

Please do not quote me as saying to remove 1" of pitch. I was simply speaking out loud, while asking for a re-pitch price and MORE importantly - SOME GOOD DATA. Your wife and kids with you data is just fine for me...and your full crew of buddies and stuff.

5500 rpm's at 22mph and a 2.41 gearcase reads more like a prop with ~11" of EFFECTIVE pitch. that's with 8% slip.


EDIT: FYI... a 9" effective pitch prop with 8% slip and 22mph, would put you at 6762rpm and on the correct side of that motor's power curve.

 

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

edit: duplicate post... sorry

 

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Please do not quote me as saying to remove 1" of pitch. I was simply speaking out loud, ...

No problem, I was using it as an example as well - referring to the type of work that I believe that shop does by the hour, but I understand your concern if I were to go and say that was the exact answer... but it may end up being
I will have to have a chat with them first though of course. If I remember correctly their first thoughts before were to try to get the motor up out of the water more without ventilation.

EDIT: FYI... a 9" effective pitch prop with 8% slip and 22mph, would put you at 6762rpm and on the correct side of that motor's power curve.

Thanks!! for the FYI... I didn't really know what you meant by the calculations other than to assume from previous context that it was a bad thing for my motor.

 

[Sea Rider]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Sea Rider, you're thinking of the 9.9 for 5K-6K rpm range. The 15 has a range of 5500-7000 rpm, as previously mentioned. Let's not forget that we're dealing with a 22 year old motor here.

Ooooops, skipped the manufacturing data, used to have a 96 Evi 15, that one was rated to 5-6 K at wot. Probably OP won't find a suitable prop that delivers full or near 7 K wot rpm.

Happy Boating

 

[jestor68]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Oh, and a friend mentioned that maybe I needed to run half a can or so of sea-foam through the carb to help get it all ungunked after sitting. thoughts on that maybe it is an "22 year old engine" issue that's been sitting a lot for the last 2 years and a lot of years before that? I did rebuild the carb and replace the water pump and thermostat when I got the boat about 3 years ago, but it has sat quite a bit in the last year and a half.

Thanks.

My reference to a "22 year old motor" hints at the fact that it almost certainly has lost some compression and power. Have you checked the compression?

 

[jestor68]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

It appears that we're going in circles here because some basic calculations using what I believe to be realistic slip percentages for an old tin riveted boat(10-13%) indicate that his motor should be turning well over 6000 rpm to achieve the stated 22 mph with a 9-10 pitch prop.

I'm suspecting that his E Bay tach isn't reading right if it's just showing 5500 ish rpm at 22 mph.

 

[dazk14]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Ooooops, skipped the manufacturing data, used to have a 96 Evi 15, that one was rated to 5-6 K at wot. Probably OP won't find a suitable prop that delivers full or near 7 K wot rpm.

Happy Boating

How do you arrive at that suggestion? The OP is confused enough as it is.

Edit:FYI- The owner has been using a gps for speed and getting 22mph - to save you from having to re-read.

 

[dazk14]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

My reference to a "22 year old motor" hints at the fact that it almost certainly has lost some compression and power. Have you checked the compression?

While some loss is normal, unless you don't believe his 22 MPH GPS speed with himself and half his garage in the boat on a 14'er, he's making good power.

2 strokes make dynamic compression at high rpm's, so often a compression loss is more noticeable during acceleration, but that's a different topic.

All the stainless props I have seen and fitted to the small motors(10-15hp), were pitched/acted higher than stamped on the prop. We all know the number stamped is just a ballpark figure.

I agree that it's prudent he confirms an accurate tach reading.

I don't want to confuse Can'tfish. It sounds like he has a nice little family and with his penchant for analyzing and writing, he may crash the site using up bandwidth. Not to mention, his kids don't want to wait 3 more years to get that boat on plane with "Uncle Buck" on board.LOL

 

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

I'm suspecting that his E Bay tach isn't reading right if it's just showing 5500 ish rpm at 22 mph.

I'll get some better data in the next few weeks I hope. This last update was after first time boat was used in a year and a half with the new tach, and having the wire where it wasn't trying to read from both plug wires (I attached the single wire one to the same place I had the original which was the two wire type - 2nd wire being ground). The first one did not have a problem with picking up both plugs... Or at least I don't think so. Since we pretty much were fully loaded I didn't even bother with speed on gps or by phone app, just due to the fact it seems pointless with that much weight.
I did take a quick trip with just two kids and I and it seemed like it was running ok at what "felt like" a decent speed wot, but due to low lake levels I was paying more attention to not hitting sand bars or trees than to the tach or gps...

 

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

While some loss is normal, unless you don't believe his 22 MPH GPS speed with himself and half his garage in the boat on a 14'er, he's making good power.

2 strokes make dynamic compression at high rpm's, so often a compression loss is more noticeable during acceleration, but that's a different topic.

All the stainless props I have seen and fitted to the small motors(10-15hp), were pitched/acted higher than stamped on the prop. We all know the number stamped is just a ballpark figure.

I agree that it's prudent he confirms an accurate tach reading.

I don't want to confuse Can'tfish. It sounds like he has a nice little family and with his penchant for analyzing and writing, he may crash the site using up bandwidth. Not to mention, his kids don't want to wait 3 more years to get that boat on plane with "Uncle Buck" on board.LOL

doing what I can to learn... Sorry I get a little long winded trying to make sure y'all get the important details... it's a bit of a bad habit I guess.

On that note: I think I did test the compression right after I bought it just to make sure it wasn't a lemon... but I don't remember the numbers - it's also a pull start which seemed to give some what sporadic results in my opinion over a electric start. Anyone know what numbers I should look for? I think the thing I read said to remove both plugs, put on gauge and pull 5 times and read gauge? does that sound right? I don't remember the #s I was looking for.

Can you do compression test using air pressure in over air out when cyl is at tdc like you can on a car (or as done on aircraft engines) on a two stroke?

 

[dazk14]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Can your budget handle $77.99 for a Solas Amita 9 pitch, 4 bade prop?

Jestor - You changed/edited your post suggesting a 7" pitch to a 9". I understand why.

For clarity and continuity in a LONG thread with 1800+ reads, adding a note indicating that change would surely help our sanity.

 

[Sea Rider]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

How do you arrive at that suggestion?

As forum stated, if that oldie works 7 K rpm at wot, he should aim to achieve that rpm with him alone and lightly loaded boat to begin witth, as he starts to add weight rpm will drop accordingly. To find available prop pitches or not is a different story....

OP, what's your engine rpm reading at idle ? Wrap pick up signal cable on just one spark cable, if at both could pick unwanted signal from the other and not read properly. Some induction tachs have 1 wire and no ground wire, some 2, signal + ground wires.

Happy Boating

 

[sc76]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

I think you are overthinking it. A 15 on a 14' tinnie is about right. The discussions around here are for bigger rigs.

If you are frequently carrying loads and don't mind too much speed when alone, go up to a 25. but foils are a waste, trim tabs are for bigger boats, props may make some difference but factor in the cost, it may not be worth it.

3 people in a 14' boat is not likely to do much planing. One trick to help get up on a plane is to run over shallow water. Play with shifting your passengers around, too.

Enjoy what you have.

I have a 15' fiberglass with a 15 hp merc. it plains nicely,i have a 1976 surecast semi v

 

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

:doh:

OP, what's your engine rpm reading at idle ? Wrap pick up signal cable on just one spark cable, if at both could pich signal from the other and not read properly. Some induction tachs have 1 wire and no ground wire, some 2, signal + ground wires.

Will idle with hose earmuffs be a valid measurement? Otherwise, I'll have to check idle speed next time it's in the lake. Or if I get time I'll fill a trash can with water and check it. I'm assuming that in neutral for idle it wouldn't really matter if submerged or using earmuffs


Yes, it is now a single wire induction tach - wrapped around bottom plug wire with sever inches between the wrap and top wire. (as noted formerly - it was on top wire & reading double the expected #s-
When I was just testing it before last trip I had the thought that it was picking up readings from both wires due to proximity - which is why I don't really have any other data that's probably valid right now - I didn't think to record idle speeds. Was only looking at wot... :doh:

 

[dazk14]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

Ooooops, skipped the manufacturing data, used to have a 96 Evi 15, that one was rated to 5-6 K at wot. Probably OP won't find a suitable prop that delivers full or near 7 K wot rpm.

Happy Boating

I asked how did you arrive at that conclusion...

I will supply some extreme figures for you using an iboats available 7" pitch example. BTW- it uses the same props as your old 15hp did (if you weren't aware).

speed 22mph (his current gps speed)
gear ratio 2.41
Prop pitch 7"
slip 10%
---------
yields rpm of 8887 even at 0% slip (which is impossible) yields 8000 rpm, which would throw a connecting rod in very short order...
which without a motor, the OP would start a new topic on how to select the correct oars and 3yrs later and 1900 reads, the kids would still be paddling with their hands. LOL

 

[Can'tFishEnough]

Re: please help sort out options... prop, hydrofoil, trim tabs, or other? (15hp Evinr

which would throw a connecting rod in very short order...
which without a motor, the OP would start a new topic on how to select the correct oars and 3yrs later and 1900 reads, the kids would still be paddling with their hands. LOL

lol, I'd probably ask about trolling motors before oars - but honestly, it really wasn't my intention to revive the old post. I thought I was saying the issue was fixed- ventilation is nearly nonexistent now due to the cupping... I had no idea I was still in the under power or bad pitch zone. I didn't even look at the # of reads when I updated it. Didn't know i was still in a can of worms (fishing pun intended)...

Thanks to all for suggestions - will work on data as soon as I can. with 3 young kids it's just hard to get to the water alone...

 

[Can'tFishEnough]

quick update... finally had time to take out with just me and minimal equipment week of the 4th... no dice on good data for speed and such -
Fired it up with ear muffs on to get warm for compression test 6 pulls both cyl @ 110 (gauge was not super high tech since the needle covered 5psi alone, but anyway). Put it in the water and tried to throttle it up and the engine ran like a cow in mud. It only got worse through the week. Got home on the 7th re-did compression test top cyl at 30psi.

Long story short, blown head gasket at 6:00 on Top cyl. In the process of replacing head gasket, and while I'm at it the water impeller incase that was the cause. Also plan to re-adjust the carb and may replace fuel pump diaphragms (they may be original not sure). Data still pending - though I doubt that anyone is holding their breath. But at least that seems to give a bit of closure to some the RPM issues I was having in March.

 

[Can'tFishEnough]

Final update on this thread- last year Apr/May 2015, Got motor running well again - took on lake with optical tach from harbor freight with kid in front (to make sure I didn't hit anything while turned around - lightly loaded boat was traveling at about 18-19 mph motor was running at around 4800-5000rpm. So I was deciding to go ahead and get a lower pitch prop when.... I ended up with a whole new (to me but old) boat.

I was looking around online at the local swap site for a 18-20 hp motor and found a '94 16.5ft Alumicraft with a '94 25hp 10x15pitch prop Evinrude for a good deal. The guy who had it just wanted the money for vacation rather than to spend the time fixing up the boat that had been sitting for at least 3 years. We got the motor to caugh out some smoke so the ignition was good - compression was good, the carb needed to be cleaned and fuel lines replaced in a bad way.

A couple new trailer tires later - I got it home, fixed it up, and took it out- long story short, it was only lumbering along running at about 4000 rpm. Because of the advice here I when ahead and staret out with a new prop. The local prop shop had an 11x9 that he sold me for a decent discount because they had it in stock for a few years just collecting dust. With this one it would run up to around 6000 rpm (though I did not let it stay there long). I had the shop re-pitch it to 11x11 and it is working nicely. Might have them go back down to 10.5. It's still a little under powered to get the speeds I'd like, but we have a lot more room for everyone to go out to the lake for the afternoon.

So all that to say - Now that I decided to bite the bullet on a different prop for this boat, I believe those on here who said re-prop were right. That change in pitch made a huge difference in performance. Thanks again.
(As of this spring 2016 the 15hp and 14ft boat have now been sold and at a pretty good profit- now I can use that to pay back savings for the other boat and fix it up a little more. So now, on to other forums on deck and foam repair... )

!!!THANKS AGAIN to all who tried to help me. I have learned a lot from you on this thread!!!:joyous::joyous::joyous: