25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

[reka12]

Hi all: We modified a boat this summer, it is a single hull 14' fiberglass SeaCraft standard fishing boat. We put in a deck, foam, center console, casting deck etc. and got hold of an '03 25 EL remote Merc (not a bigfoot). The motor came with a 10x13 aluminum prop. The motor is rated at 6000 rpm. The cav plate is 1/2" below the hull of the boat and cannot be raised any more without modifications. Currently, at WOT we can reach 7000 rpm, but that was only done during the initial testing. We are careful to only run to 6000 rpm. The hole shot is great, it just goes onto the plane. On the GPS the boat will run 24 mph.<br /><br />Any advice as to what to try next? We love the hole shot and I would guess that would be a trade-off for a couple of mph. Your thoughts would be appreciated. <br /><br />The rebuild can be found at the link in my signature.

 

[walleyehed]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

I believe I would be looking into a 15-16" pitch AFTER I verified the tach was correct.<br />I have a funny feeling the tach may be set to the wrong position...

 

[reka12]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

Well, I checked the stettings a couple of times (Teleflex set to 4-pole). Mike

 

[walleyehed]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

Mike, if this 25 has the 1.92:1 gear ratio, the tach is WAY off. If we have a known GPS speed of 24mph, the tach is quite a ways off.<br />At 7000RPM with a 13P figuring a conservative slip ratio of 18%, you should have a speed of 37-39MPH.<br />It seems as though everytime this issue presents itself, it's with a teleflex tach.

 

[reka12]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

Thanks Kenny. According to the manual, the gear ratio is 2.25:1. The GPS speed was at 6000 rpm. How does this go into the calculation? <br /><br />I will check the tach out further this weekend. I know when I go to the prop selector on Mercs website, the numbers don't jive with what I am seeing. Luckily I will be with a diehard Merc mechanic this Thanksgiving and he should be able to tell me whats up. I will keep you posted.<br /><br />Mike

 

[walleyehed]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

The numbers fit perfect if it's an 11 pitch prop???<br />If it IS a 13, we have either 1, a massive slip problem at WOT, which I seriously doubt, or 2, the tach is off about 800-1000RPM.<br />Can you verify the P/N of the prop???<br />I once had a wise man tell me to be careful around those Merc "eggsperts"...

 

[reka12]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

Walleyehed (Kenny): Sorry for taking so long to get back with you. The P/N that we think we were able to make out (thank God for the eyes of a 14 year old) is: 48-T9640A40 13P. I measured the diameter at around 10". Thanks for your help.

 

[reka12]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

I think that PN might be 48-19640A40. Mike

 

[walleyehed]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

48-19640A40= 10-3/8X13<br />Std equipment on the 25...<br />The slip ratio is extremely high for a 13P with the numbers you give. We have a known GPS of 24, and a known gear ratio, and if the prop is not worn out or has been worked, we know we have what should be 13 pitch, so if we figure all of the variables that remain, it leaves only the tachometer.

 

[b.gagnon]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

If my eyes are seeing correctly you have a very big problem!<br />It looks like you bought an x-long shaft motor. If so you have three options.<br />1.Sell the motor and get a new one.<br />2.Change the shaft length (usually not worth doing)<br />3.Buy a jack plate, but I would not recommend this option due to the way you fixed the transom. It will end up putting more stress on the top half of the transom and I don’t know if you repair could handle that.<br />Also your tach must be way off!

 

[cobra 3.0]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

I had a 30 hp Johnson on a 16 ft Aluminum boat with floor boards(weight unknown of the boat) ran about 30 mph with a 13" pitch prop. Your boat looks heavy, I highly doubt that a 15" pitch prop will work efficiently. A 15" pitch on my boat was very sluggish with more than one person and I had it repitched to a 13".<br /><br />What you haven't given us is the speed full out, which I would guess will be close to my 30 mph give or take 2-3 mph. In conclusion, I think the prop is correct and your rpm gauge is way off.

 

[ricksrster]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

Is 4 pole the correct setting for that motor?

 

[reka12]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

B.Gagnon: Yes it looks long on the transom but it is for sure a 20" shaft. Right now, the cav plate is 1" below the hull. When that picture was taken, we had not raised up the motor yet. We started with a 17" transom, raised it two inches (should have raised it further) and made up some of the difference by raising the motor. I know it still should go further and we will do that over the Christmas break.<br /><br />Cobra: WOT (7000 rpm on the tach) the GPS shows 28mph. I am guessing that you all maybe correct on the tach. I will be trying a Merc tach over the holidays.<br /><br />Ricksrster: Good catch. It is an 8 pole stator. The red is 12. The 4p that I mistakenly referred to was the switch setting for the Teleflex tach.<br /><br />All: I really appreciate your comments and observations. We are going to raise the engine a couple more inches, try a different tach and two different props. Maybe I wil not get anymore out of the little 25. I am not really complaining about the performance but was wondering if it was correct and if I could tweak it just a little more. <br /><br />I don't think the boat weighed more than 400 pounds when we started. We calculated we added maybe another 50 in the rebuild plus another 117 pounds in the engine, and another 20 or so in stuff. But like you guys, maybe I can get just a little more and wanted to get your opinions on the tach observations. <br /><br />Your input was very helpful and I will get back with you on the results.<br /><br />Mike

 

[b.gagnon]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

Can you post more pictures of the motor setup? There may be other ways to gain an Inch or two. You are most likely loosing a few mph by having the motor so low, but some hulls like to run that way. Great job on the boat! Your project is a great example of turning a small fishing boat into a fishing machine! Check out Tiny Tach’s they are about $40-50 and take only a few minutes to install.

 

[reka12]

Re: 25hp '03 Merc, 14' Custom Built Center Console Prop Advice Needed

B: Had a chance to toy around with it a little. The tach is off by about 750 rpms (reads high). I can probably go to a 14 or 14.5 pitch, but frankly it is fine for what we do. We know that we got to keep it below 6750 rpms on the tach to stay below the rated max rpm of the motor. By the way does anyone know if these little Mercs have a rev limiter? I know for a fact that the Merc 20 Jet did.