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Posts: 770
| Guys, I'm running a 2010 1750 Fishhawk side console with a 115 Merc 4 stroke. My prop is a SS appolo xhs 13 1/8 X 19. At WOT I'm hitting roughly 5600 rps and top speed of 28- 30 mph.
I have talked to guys with 60 hp on simialr rigs getting the same speed. Now I know my rig isn't built for speed but I have also talked to guys running 1750s W/ 115s getting 42 mph.
Also i feel like I'm not getting as much trim as I should be ( trimmed to a certain point and I rev high and drop speed.
Is there anything else I should be looking into?
I'm not very knowledgeable on props so I was hoping for some recommendations on props to try (size and brands)
Also what is my prop worth used (great shape) and what will a decent new prop cost?
Also my speed is GPS
Thanks for your time!
Read here for reference:
http://muskie.outdoorsfirst.com/board/forums/thread-view.asp?tid=27...
http://muskie.outdoorsfirst.com/board/forums/thread-view.asp?tid=24...
Edited by T3clay 5/1/2018 2:20 PM
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Posts: 3484
Location: Elk River, Minnesota | Hiya!!
If my gut instinct is correct you are about 400 RPM's below your maximum RPM for the motor, and if you are lightly loaded with the numbers you have supplied, a prop change will definitely be in order. Would I also be under the correct assumption you are running an aluminum prop and the motor is mounted flat to the transom or 1 bolt up?
If the two questions are yes (flat on transom or one bolt up, and running aluminum), here is what I feel would be some things to try:
If staying Aluminum, drop to a 17 pitch prop, load the boat only with your equipment, and fill the boat with fuel. The change to a 17 pitch should bring your RPM's UP by about 400 or so, but I have a feeling it will be more than that. If the motor is mounted flat to the transom, raise it up 1 hole. A great prop to try here is to go to SOLAS propeller and order their aluminum. It is a specific squeeze-cast design which allows for a thinner blade for better performance and the blades are progressively cupped to grab really well with higher mounted motor positions. Something like this you could move your motor up to the third hole and probably get away with it.
Many times, when you reach a point where your motor is over-propped, it will drop RPM's significantly. I had a 90hp Johnson 2 stroke that I found worked best with 18 pitch and ran to max RPM (5500 rpm), but tried a 20 pitch just to see what happened....I could not reach 5000 even with trimming... It was just too much prop.
If you were to test stainless props, you could also go to a 17 pitch, BUT...go to a prop with higher rake with tip/trailing edge cupping. With this change, raise your motor to the highest position possible. The reason for this is a highly raked and cupped prop will hold the water much better at higher positions than a standard aluminum, thus the height setting will offset the switch to steel. The material change alone from aluminum to steel will normally drop your rpms by around 200 or so, but each hole up off the transom is roughly going to gain you back about 100 rpms each hole. Good props to try are the older michigan Rapture (it's no longer made), Michigan ballistic, Solas titan (I believe that is the steel..if not, its the amita), I'm unsure of what mercury offers in the midsize gearcase...I don't believe they offer a tempest in that hub size, but if they do, that is a GREAT prop to try.
No matter what you try, there are always trade offs in selecting the prop for your rig, and there is a bunch of testing that goes into it with different diameter, pitch, rake, cup, material, etc. Moving a motor up increases speed and prop slip, but decreases handling. Changing to steel increases handling (to a point-depending on prop design) and many times allows you to move the motor up without losing handling, but gain speed.
Lots of variables here to consider and no doubt I have gotten a touch long-winded.
I will say that holeshot with the 4 stroke will not be as good as a typical 2 stroke, so going to a lower pitch will help your holeshot if you have found it is not the greatest.
Steve
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Posts: 770
| This is how it's mounted and it's a stainless prop
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Posts: 770
| Also I can almost hit 6000 rpms but at WOT I have to trim way up and I start loosing speed. So for example if I open the throttle wide open and trim up my speed will increase until I hit 5600 RPMs if I continue to trim up past 5600 my speed drops in my RPMs jump very quickly
Edited by T3clay 5/1/2018 5:19 PM
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Posts: 1209
| You should get more speed than that, but in my experience boats like this don't need a lot of trim, so you know the point where it's fastest is probably a good point. Are you sure your getting wide open? Or have you looked at the spark plugs? |
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Posts: 770
| I haven't checked the plugs and I guess I assumed I was getting.wide open. I don't have any reason to believe I'm not. I just figured my mount height or prop was off. It's been checked 2X in the last year by the dealership so I'm sure the plugs are good. How would J go about.checking if I'm getting wide open? |
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Posts: 3484
Location: Elk River, Minnesota | Hiya,
Ok.. first question with the prop you have... what brand and model is it?
Second, how much trim have you gone before blowing out? In many cases, half trim on a gauge is pretty standard. Any higher and you blow out as the prop loses grip.
Now, here's the good news. Being you are in a steel prop already, there is no doubt in my mind your motor can come up off the transom more. I'd start by moving it to the highest position off the transom and test. This should gain you about 250 to maybe 300 rpms depending on the prop. If the prop is a stock steel, you'd be well served in getting a different prop with more rake and cup. The combination of those two items will allow you to trim less, yet get better results in bow lift and handling.
If you are close to the twin cities, I'd help you adjust the motor height...
Steve |
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Posts: 770
| Thanks Steve! Right now I can't get to the halfway point.on my trim gauge but I don't think too much into that. Maybe it's just the lack lift that's making me.feel like the trim is off. This is my first alum. Boat coming from multiple glass boats so the feeling is alot different. It's a Michigan wheel Apollo prop.
Edited by T3clay 5/2/2018 6:30 AM
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Posts: 3484
Location: Elk River, Minnesota | Hiya,
The apollo series replaced the Rapture, so they are fairly similar in design. I would say try raising the motor and see what that does for you. I don't think that prop is going to be the best fit in the end, but testing it at a higher position definitely cannot hurt.
I would tend to agree, though that you should be seeing higher numbers on your speed. I am assuming this is GPS speed that you gave at the beginning yes? The only other thing I can think of would be a tach setting is off.
I'm doing some other checking as well...do you happen to know the gear ratio of the motor off hand? I tried some prop calculations with your 5600 rpms and everything shows you should be upper 30's to 40 in that rpm range, which is why I'm curious about the tach setting as well...
We will get this figured out....
Steve
Edited by VMS 5/2/2018 6:53 AM
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Posts: 16632
Location: The desert | I really need to drag my boat down to Steve the prop wizard. I know I'm not getting all the performance out of my boat. |
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Posts: 688
Location: Already Gone | I'd also like to say Big Thanks to Steve now for all of the free advice he's given us through the years. Cool stuff. |
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Posts: 73
Location: Cedarburg, WI | Mark Hoerich - 5/2/2018 7:59 AM
I'd also like to say Big Thanks to Steve now for all of the free advice he's given us through the years. Cool stuff.
x2. Thanks Steve. |
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Posts: 770
| Looks like my WOT RPM range should be 5800-6400 2.07 gear ratio
Edited by T3clay 5/2/2018 11:26 AM
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Posts: 532
| Somthing isnt right, it may be your tach or speedo
5600 rpm / 2.07 gear ratio = 2705 prop shaft rpm
2705 prop shaft rpm * 19" pitch of prop = 51395 inch per minute.
51395/12= 4283 feet per minute.
4283 x 60 (minutes in one hour) / 5280 (feet in a mile)= 48.7 mph theoretical top speed.
48.7 x .85 (average prop slip) = about 42mph top speed.
average slip is 15% your getting like 40%. very poor for your set up.
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Posts: 3484
Location: Elk River, Minnesota | Thanks everyone!! The comments are greatly appreciated!!
TClay,
If your max rpm is 6400, a drop in pitch will definitely be in order. With the height change, you would gain about 300, then going down in pitch to a 17, you will gain another 300 or so as well.. this rules out a tach being off and definitely puts it at a pitch issue.
If you have access to any friends with props to try or go to eBay and see what you can find, you'll see a magnificent increase in performance going down in pitch and up in height.
Running some quick numbers on a 17 pitch, 6300 rpm and 12% slip theoretically you should be at 43 mph. You get to 41 or 42 you are sitting well...and... you will have much better holeshot... the merc 115 is not fast out of the hole to begin with (from my experience with them), so this will be a great step up with it as well...
Steve.
Edited by VMS 5/2/2018 12:14 PM
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Posts: 532
| How are you getting your speed? and what brand or style tach are you using?
VMS do you think he will gain 700 rpm by droping 2" of pitch, its almost double the rule of thumb.
I almost have to question your instruments at this point, I am not saying dropping pitch wont help, i think it will.
The difference in the math i posted earlier has a concern that one of the supplied numbers is not correct.
If it were me i would find why the numbers are not closer to matching before trying a different prop.
You tach could be off and your at 6500 right now (not saying you are, useing an extreme number as a example), or your speedo could be reading 30 but your doing 40. The formula isnt close so a number is wrong.
Edited by anzomcik 5/2/2018 1:22 PM
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Posts: 770
| My speed has been based off of GPS from my locaters, hummingbird 899 and helix 7. I may be off on my numbers, as I'm just going from memory. I will try to get the boat out this week and write everything down. I can't thank you guys enough for the imput! |
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Posts: 3484
Location: Elk River, Minnesota | anzomcik - 5/2/2018 1:00 PM
How are you getting your speed? and what brand or style tach are you using?
VMS do you think he will gain 700 rpm by droping 2" of pitch, its almost double the rule of thumb.
I almost have to question your instruments at this point, I am not saying dropping pitch wont help, i think it will.
The difference in the math i posted earlier has a concern that one of the supplied numbers is not correct.
If it were me i would find why the numbers are not closer to matching before trying a different prop.
You tach could be off and your at 6500 right now (not saying you are, useing an extreme number as a example), or your speedo could be reading 30 but your doing 40. The formula isnt close so a number is wrong.
Hiya,
I think you might have missed a couple of things I stated from earlier posts... Raising the motor will be around 300 or so, and going down 2 inches in pitch will be around another 400 give or take....thus the roughly 700 rpm increase...
The numbers are very very general as every boat is a bit different...even boats of the same brand, model, year, and even one right after the other off the line.
I have also mentioned the tach might be off, but at this point I'm not so sure... until we get some changes with the prop and height made will we see... I'd rather not send him to spend money that might not prove a thing, whereas doing a few things at home to see get him started without money.
There are a huge number of variables in this...there is even potential that the hub is spun resulting in loss of speed, or the prop just does not hook up very well at all whatsoever... Only way to know is to test and try things...
There is also a point of diminishing returns with props as well... when over pitched, the motor just cannot handle the load...it can't trim up? it cannot get even close to desired rpms.. I have tried this going from an 18 pitch to a 20 pitch on my old boat. 18 pitch would get me to 5500 rpms but the 20 pitch wouldn't even reach 4800...the motor just could not do it... Given he is not 100% sure of his numbers, all I can go off of are his numbers. The numbers I supplied above are putting the motor in a 17 pitch at 6300 rpm with a 12% slip. I agree with you that the numbers given don't add up very well.
Steve
Edited by VMS 5/2/2018 3:57 PM
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Posts: 770
| Mounting pictures, clearly too low
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Posts: 770
| The motor is trimmed all the way down in the last picture. It appears that the motor used to be mounted to holes higher than it currently is, based on wear marks on the mounting plate. My local Marine shop said it would be $70 to raise the motor up. They were also going to see if they have a used prop in 13 x 17 |
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Posts: 3484
Location: Elk River, Minnesota | Hiya,
It stinks you don't have slots on the lower portion of the mounting plate...if you did, you could do the raise of the motor right in the driveway. With individualized bolt holes, a lift is needed of some sort unless you have a couple of buddies who are willing to balance the motor while you remove the bolts raise the tongue of the trailer, then reinstall the bolts.
Most definitely too low... In many cases the anti-ventilation plate can be upwards of 2 inches ABOVE the lowest point on the transom without issue... Reason being....the water starts to fill the hole back in that the boat made...
Steve |
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Posts: 770
| Steve, do the bolts need to be re siliconed if I only remove the nuts? I'm sure I can find some guys to help me balance the engine. But can the keel really support that much weight? |
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Posts: 3484
Location: Elk River, Minnesota | Hiya,
The project is easiest to remove the bolts, clean them up and reinstall...that way you are not moving the trailer away from the motor....so yes...you should re-seal the holes as you go. It's a nice preventative measure as well because if the motor was lowered and the previous owner/dealer didn't do this before the sale, you could find down the road some soft transom material...that is not an easy fix...
If you get a couple of buddies to help, get some wood blocks and use them to help balance the motor using the anti-ventilation plate. support the plate on both sides (prop off here would help big time), have the guys help keep balance, remove bolts, raise the tongue of the trailer until the bolt holes reallign, then reinstall the bolts.
Definitely be sure to lower you jack as far as it can go before you start. The jack needs to move a long way to get the little adjustment in the rear you need.
Steve
Edited by VMS 5/3/2018 12:45 PM
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Posts: 770
| Steve do you have a lift? |
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Posts: 3484
Location: Elk River, Minnesota | Hiya,
Unfortunately, I do not. Are you close to the twin cities?
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Posts: 770
| I'm down by rochester |
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Posts: 770
| Steve I'm going to raise the motor myself, how much should I raise it to start, what's your best guess? |
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Location: Northern Illinois | $70 bucks isn't bad. Is it worth the headache without a lift? |
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Posts: 770
| I have a tractor that should do the job |
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Posts: 3484
Location: Elk River, Minnesota | If you have a lifting ring for the motor that would work fine.
I would go up to the highest position and see what you find out. Worst case is you have to drop it one slot, but I would bet that will be the most you'd have to drop it.
Steve
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Posts: 770
| That seems like a long ways. Am I going to run into any issues with my cables being to high? And what will be the issue with it being to high?
Edited by T3clay 5/9/2018 6:58 PM
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Posts: 3484
Location: Elk River, Minnesota | Hiya,
Cables and things should be just fine. you are going up about 3-1/2 inches to possibly 4 inches, but as you showed in your previous pictures, your anti-ventilation plate is about an inch below the bottom of the boat...
Steve |
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Posts: 770
| Well found out there was a sticky spot on my throttle and I was not getting g WOT. Got the boat up to 41.5 MPH last week but I am still having issues getting the boat to plane. My spray is coming off the front 1/4 or 1/3 of the boat. I'm trimming up as far as I can before my prop starts to blow out. Any recommendations? |
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Posts: 3484
Location: Elk River, Minnesota | Hiya,
Sounds like you need to get a prop that has more lifting capabilities, but 41.5 on that boat with the 115 4 stroke is getting close to the best you will see....
If you have not moved the motor up off the transom more, the lower unit is still holding you back a touch as well. With more lower unit out of the water, the less drag you have, thus more speed. I believe this will be a big part of the equation here...
I do tend to think you need a prop that has more tip cupping to it to help lift the bow and trailing edge cupping which would lift the stern more as well...
Something like this prop on the link below is worth a try, but you would be much better suited to find a dealer that has a demo prop program so you can go out and test different props to find one that will do what you are looking for it to do.
Although you have a mercury engine, if you can find an exchangeable hub system that fits an older Michigan Rapture, Ballistic or BRP Raker propeller, you'd have some options to try...
The raker is a great prop, and it has 15 splines, but most likely would not match up unless you can find an exchangeable hub system for it. The older pressed hub models will most likely not fit.
Steve |
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Posts: 770
| Thanks Steve, I'm totally happy with this speed, it would be nice to get a little more lift out of the bow though, how would raising my motor affect how much i am able to trim?
Also I don't see the link you mentioned above
Edited by T3clay 5/22/2018 11:14 AM
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Posts: 3484
Location: Elk River, Minnesota |
Hiya,
Having more lower unit out of the water may allow the prop to lift the entire boat more, and potentially let it do a more efficient job trimming the boat. In some cases, getting to higher rpms than where you are now allows the prop to stay hooked up better, thus allowing the trim to work more efficiently as well. It's kind of like when you you have too much trim at lower throttle settings that the boat will begin to porpoise. At speed, the prop can hold the boat up, but at lower throttle settings, the prop is unable to.
You may also find if you have a bunch of gear in the bow, that may be playing a factor as well in how well you can trim. If you have a full livewell up there, two batteries, and gear, it will be harder for the motor to trim the bow up.
IF you wanted to really tweak things, you could get a manual set-back plate to mount the motor back off the transom just a touch further. This would change the center of gravity of the boat more to the stern, thus giving the motor more ability to lift the bow with less trim.
And yes...I forgot to post the link..
http://www.ptprop.com/index.php?page=shop.product_details&flypage=s...
Steve
Edited by VMS 5/22/2018 12:03 PM
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Posts: 770
| Thanks Steve, I'd like to see if I can get some lift without having to buy a new prop. I also would like to have the motor lifted but I don't want to have to move it more than once. I guess I'll see if I can get it moved and see if that gives me any more lift |
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