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I need some advice, I had a 1970 16' hull rigged Montauk-style with a 75 HP Honda, turned 5200 RPM, now I took everything off that hull and put it on a 1978 Montauk with a 4" fixed (Bob's Machine Shop) jack plate, motor is on top hole and not slipping. I'm only getting 4700 RPM and I have to trim way up to get that. Any suggestions or thoughts on what's going on here? Thanks, PG

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Don't understand, "Motor is on top hole" ???

Is the motor mounted all the way up and the bolts are in the bottom holes of the engine bracket?
Or,
Is the motor mounted all the way down and the bolts are in the top holes of the engine bracket?

After we know that, then we need to know more about the jack plate or where the cavitation plate is in reference to the bottom of the hull.

Why a jack plate?
So you didn't have to drill anymore holes in the transom?
http://www.whalercentral.com/articles...icle_id=82

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Paul,
The outboard is in the top hole on the jack plate, but which hole on the outboard mounting bracket, top as well? I believe your engine is too low, you need to move up to the second, possibly the third hole on the engine bracket. If you look at your outboard when running at speed, I believe you'll find that the cavitation plate is buried and not riding above the water.

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The motor is all the way up, bottom hole on the motor. Prop is a stilletto 13 3/8 x 19, I've had the motor down 2 holes and get the same RPM's. I mainly put the bracket on to get the motor off the refinished hull, it drools a little rust from around the bracket at the top of the vertical pivot tube

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First, there's the hull difference. Aren't the 16s a little slicker in the water than the smirked hulls?

The 16 also may have weighed a little less if the console and seat you used was Todd or another aftermarket. Any bottom paint on either? Maybe the 17 is a little more damp?

500rpms is a lot to lose, but many factors will add up and exacerbate the issue aside from hanging the motor. The prop seems to be maybe a bit steep as well. I know Tom W Clark has recommended Stilletto props that are 13 1/4 x 15 for Montauks with 90 hp OMC/BMC motors. I'd ask him, he's a prop guru and his advice was spot on for me.

Don't get discouraged, you'll get it.

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Thanks Bo, I would love to here what Tom would say about my situation. Tom, would you please give me some advise? I borrowed a 13 x 17 prop from a friend last night and will try that today, I also will take a closer look at the tach, I have a couple of spare tachs I can compare, thanks again

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Paul,
where is the cavitation plate in relation to the keel?

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It is 3" above the keel, but it does not appear to slip or blow out when I nail it.

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If the plate is out of the water on plane you may just have to drop back to a 17pitch prop.

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You are overpropped. Use a lower pitch propeller.

Kamie wrote:

No, that is illogical. He needs to drop pitch because the engine speed is too low at WOT. It has [almost] nothing to do with where the AV plate is.

Having the (AV) plate out of the water is a good thing and increases, not decreases, the RPM.

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Tom,
I am aware that having the plate out has nothing to do with the prop pitch, it is a confirmation that the outboard is mounted at the right height. With a jackplate and a 4 inch setback 3 inches above the keel on the trailer may or may not put the outboard at the correct height on plane. logically one of two things are wrong, either the outboard is too low or the pitch too great. Confirming that the plate is out of the water on plane, points to the pitch of the prop and if that is the case, I would suggest he drop to a 17pitch. If the plate is not out of the water at speed, then I would raise the outboard if possible, if it is not, then his only option is to drop down to a 17 pitch prop.

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ok, I borrowed a 13x17 prop, I'm goinng to try it today. What will a 3/8" drop in diameter do? Thanks

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Paul,
See if the pitch gets you closer to max RPM's at WOT. Once you nail down the pitch, then you can look at different props. I believe that your Honda should run between 5000-6000 at WOT with max HP at 5500. Depending on if the 17 puts you in the ball park, you might drop down to a 15 and get closer to 5500 to 6000RPMs.

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I have no way of determining my speed, what will a 2' drop in pitch do to my top end?

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Paul,
We have really no choice in selecting a diameter in a prop basically.
We can only choose the pitch... 15 pitch, 17 pitch, 19 pitch, etc....
The engineers figure out the diameter according to the pitch for a particular manufacturer.
Different prop manufacturers even have a different diameter than other manufacturers even if they are all 17 pitch.
We can't say we want a 13 1/8 x 17
or a 13 1/4 x 17
or a 13 1/2 x17
The general public buys props by the pitch and brand...

The RPM's is what you really want to look at rather than speed. Your engine manual states that the engine should max out between certain RPM's at top speed... Whatever the top end speed is, that is what you get...

However, generally the smaller pitch will give you a better hole shot.
The larger pitch will give you more top end speed.
Being over propped isn't good as your engine will never get up to the recommended RPM's when running and isn't good on the engine as it is working too hard.

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Launched the boat this morning, I can get a solid 5100 rpm and occasionally hit 5200, I'm sure I can have my 19" prop changed to 17", should I shoot for 16" ? Thanks

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Paul,

Can you tell us exactly WHAT 13" x 17" propeller you tried?

You say you have a 13-3/8" x 19" Stiletto, but Stiletto does not make propeller in that size. Can you confirm the part number?

At nay rate, I almost never recommend changing pitch of an existing prop, an NEVER as much as 2 inches of pitch. It is always much better to just get the prop that you really need.

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Tom, I pulled the prop off a 130 Yamaha, it's a 13x17-K2, #805. Mike Hood's prop shop in Houston did not seem to think it was a big deal changing pitch as much as 2 inches. He actually recommended dropping 4" in pitch, but said he could not change a prop that much. Don't you think a 15" prop would to much of a drop, especially after seeing the improvement of a 2" drop in pitch. Why are you against changing the pitch on a prop? Thanks

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Paul,

What does the prop off of a 130 Yamaha have to do with this discussion about the prop for your Honda????? Or am I missing something???
We need to know the numbers on the prop you have now on the Honda 75 this discussion is about...

I have 3 props for my boat....

15 pitch, 17 pitch, and 19 pitch....
These are all OMC props for my OMC 150hp motor...

The 15 pitch gives the best hole shot and the 19 pitch gives the best top end speed. I decided to keep the 17 pitch prop on all the time as it is a happy medium for my needs.

However, there is a big difference between brands of prop and their pitch or aggressiveness.... You need to find the right pitch prop to bring your RPM's to within the guidelines of your motor manufacturer.

I personally wouldn't change pitch on a prop at all. Rather buy a different prop and keep the other as a spare or sell it or trade it in...

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Paul,
Based on your test results with the 17pitch your prop guy is correct, you should drop to a 15 pitch. The range for that outboard is 5000-6000 at WOT with the outboard making 75HP at 5500RPM's. That should be your target RPM's.

As for changing the pitch, since you should really drop 4 inchs, just purchase the correct prop and sell your old one to offset the costs.

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The prop I have is an Attwood 335132, 13 3/8 x 19. The spline on Honda's, Yamaha's and Mercury's are the same, therefore you can interchange props if you have access to them. I wanted to try a 17" prop just to see how close it would get me to where I need to be. I used to run 35mph on my 1970 hull with this motor and prop, today with the 17 prop I could tell there was less top end, I can only imagine that I might rum 30 mph with a 15" prop,if that, that's a little slower than I would like. I was pretty happy with 35 mph before. I realize I'm gonna get what I get. It is a little disappointing to see this much of a difference between the two hull's

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Paul,

OK, I presume the prop you tried is the Painted Stainless Steel propeller from Yamaha. It is a good model of propeller with not a lot of rake and a semi-cleaver blade design.

[ Aside to Joe: The Yamaha 130 and the Honda 75 are both intermediate size gearcase motors and both use the same splines on the prop shaft so you can interchange them. ]

The only time I recommend re-pitching a prop is when you need a one inch change on a prop that is only offered in different pitches in two inch increments. Yes, you can change pitch by two inches, but that does not mean it is a good thing to do. You will not end up with the same prop that the manufacturer makes in the different pitch, you wind up with a compromise that you will not be able to sell later on if you need to.

The guy at the prop shop didn't think it was a big deal because he was the guy who would get the money you would spend to do this.

The Stiletto Advantage model (which I presume is what you started with) is unusual in that if will perform as if it has two more inches of pitch in comparison to most other props.

So it's really like you started with 21" of pitch with the Stiletto. The switch the Yamaha K Series 17" should have resulted in a bigger difference.

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Paul,

There is another variable here for your engine speed that is not directly related to the difference between the older hull and the newer hull.

This other variable is the "Jack Plate" you just installed on your newer hull.

If you were to mount the engine exactly like it was mounted on the older hull, then we could compare the differences between the 2 hulls.
As it stands now, we have to take into consideration that you also added a Jack Plate to your new hull which changes the calculations and evaluations...

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I agree with Joe. Yo could still have the motor too low.

At any rate, an Attwood 335132, 13 3/8 x 19 is a Michigan Wheel Ballistic model. Even on the old hull, at 5200 RPM that prop was too much for the motor.

Given the RPM drop sine then, you will really need to drop pitch and even a 15" Stiletto is not going to be enough because it will perform like most other manufacturer's 17".

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Ad the cause of the difference between the old hill and the new one, you also have to consider the effects of a waterlogged hull. Added weight will kill boat speed...and RPM.

Do you have photos of the new boat floating?

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And...are we sure there nothing done to the motor, or rigging when the switch over was made? Something that might limit throttle travel, perhaps?

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Tom, you are correct, it was a painted stainless steel Yamaha prop, it seemed to give me about an additional 500 rpm. It is a very plain looking prop, the stilletto seems like the edges have a slight curl, is that cupping. I am convinced, I need a new prop, would you mind telling me what you recommend. I don't see how my motor could possibly be to low, it is mounted as high as it can go. The top of the bracket is flush with the top of the transom, the motor is all the way up on the bracket

Joe, I have always been under the impression the raising a motor created less drag, put the prop in cleaner water, increased rpm's and improved top end, I guess I was wrong about that

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Paul,

In theory you are probably correct.

The bottom line is where the cavitation plate is when you are running the boat at speed and all trimmed out with a normal load.
The cavitation plate should be just slightly above the water. Not under the water.

Have someone drive the boat for you and take a look at the cavitation plate and let us know if you can see it or not...

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I don't know how much if any, water is in the hull, but the first time I launched the boat I paid special attention to how she sat in the water, I thought it sat perfectly considering the weight of the motor and jack plate. I would say the the bottom edge of the hull just below the lettering was about an inch below the water. I am going to launch one evening this week and will take pictures of how she sits and make note of where the cavitation plate is at planning speed. I also did check throttle travel yesterday, when at full throttle the throttle cam is in full open position, so I pretty sure I'm getting full throttle. The last 3 pictures I just posted on my personal page will show how the motor is mounted. You can also compare how the older hull was rigged in comparison to the newer hull, only the last 3 photo's are of the newer hull, thanks gentlemen, I'm learning a bunch here.

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Paul,

Motor mounting height looks good. Boat looks good. I remain perplexed as to why there would be so great an RPM drop when you switched this motor to the newer hull.

Something is funky here. Are you sure the motor is firing on all four cylinders? Have you made sure the spark plug boots are all seated?

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It runs a little rough at idle occasionally but otherwise seams to run fine, I'll check the spark plug boots tomorrow. Wouldn't it run like crap if were firing on only 3 of 4 cylinders?

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No, not necessarily.

My own boat lost three cylinders on one of its V-6 motors. That motor still ran and idled, but did not have much power.

I had the motor repaired (replaced defective switch box) and when I got the boat back, I noticed that the other motor needed a little more throttle to maintain the same RPM. It otherwise sounded and idled just fine.

It turned out that one of the spark plug wires was missing after I got it back for the shop. Boy, was my mechanic embarrassed!

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Paul,

From the photos it certainly looks like the engine is high enough...
Hopefully not too high but only running it will tell you that...

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I have gone thru the carbs and made sure that I am running on all cylinders. I picked up a 15" x 13.5" pro and only got 5300 rpm's. The Honda mechanics tell me I should be running 6000 rpm's, so I went back to the prop shop and have a 13" x 13" prop coming. I was wondering, does anyone else on this site have a 75hp Honda on a smirked montauk. I would like to know what prop they are running and what RPM's they are turning, thanks

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Tom, I got the hotdogs, thanks, I owe you. I finally took a photo of the boat launched. Can I get opinions on weather she looks water logged, it's the last photo on my personal page, thanks

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Paul,

Your personal page does not show any photo of your current boat floating in the water.

The last photo there is of the bracket and it looks like it was taken in your driveway at night.

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I think I got it posted now, thanks

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No, that hull does NOT look waterlogged.

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Thanks Tom

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Are you sure the throttle is reaching its fully open position at WOT? You've checked your cables?

There is no way that boat should require a 13" pitch prop.

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The throttle bracket is fully engaged, I would think there is no way the carbs are not opening all the way. I am so diappointed in the 13" prop, I am thinking about exchanging back to the 15" prop reguardless. I think I will pull the carb assembly 1 more time just for piece of mind. I am heding out of town tonight so it will be Sunday or so before I get back on it. Hey, did you recieve the email I sent you, thanks

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No, I did not.

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What WOT RPM's did you get with the 13 pitch prop?
I suggest you take and keep the records of the WOT RPM's for the different props just for reference.

Something is definitely not right with this setup....

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What were your results with 13x13 prop from the Honda dealer? Weight of new boat combination and WOT mph on previous boat?

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The 13x13 prop turned 5800 rpm, I didn't like it, the motor was screaming and going nowhere fast. I don't know the weight of the rigg but posted a photo on my PP to get an observed opinion if it looked water logged. I can't be sure now what the motor was turning on the older hull, If I remember right it was 5200 rpm with a Slilletto 19x13 3/8

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Paul,

How fast were you going with the 13" x 13" propeller?

What 13" x 13" propeller were you using?

There is no such thing as a 19" x 13-3/8" Stiletto propeller. There is not even a 13-3/8" x 19" Stiletto. I believe Paul has previously reported it was some other brand and model of propeller.

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Jeff Whidden at ptprop.com calculated based on rpm, prop and gear ratio that I was running 28mph.
He also calculated that I was running 30 mph with the 15" prop, sure seemed to be a bigger loss in speed than just 2mph. He seemed quite knowledgable
the 13" prop is 9CD3R13PH1150 semi clever

the 15" prop was ELD3R15 PVT145

Both are powertech props

The original prop was a Stiletto (imprinted on the side) I' sure it was a 19" prop maybe I'm off on the diameter but I don't think so. I was new in 1995, maybe they had that prop sze configuration back then

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Paul,

Sure you can use a prop calculator to estimate the boat speed, but we need to know what the actual boat speed is, as measured by a GPS. If your tachometer is off, then that explains a lot.

I saw a friend last night who has a Montauk with a Mercury four stroke 60 HP motor on it. He gets 34 MPH out of it so you can see why I am skeptical that you are only getting 28 or 30 MPH with a 75 HP motor.

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Paul,

Earlier in this thread you wrote:



Attwood is the parent company of Michigan Wheel, which what I suspect you really have (had), not a Stiletto.

Michigan made the stainless steel Rapture model in that size with that part number.

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.

This is yet another reason why I suspect your tachometer may not be reading correctly.

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Tomorrow, I'm trading the 13x13 back for the 15x13.5 prop, I'll pick up a new tach while I'm out. I'll let yll know how she does, thanks

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Paul,

Earlier you said you took everything off the old boat.
Did that include the tach also?
What brand of tach? Honda?

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Paul -- In propeller nomenclature, diameter always precedes pitch. Thus I think you meant to write that you have a 13-1/2" x 15" prop.

Also, borrow a handheld GPS while you're out, or if you have an iPhone or Blackberry, just download the speedometer App. so you can get some accurate speed data.

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I am going to borrow a gps tonight, and your right I'm tradin the 13" pitch for the 15" pitch, thanks. what does the tach pick up for signal to interpret into rpm's?

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Paul,

I will ask again.....

What brand of tach do you have and is this the same one that came off of your other boat?

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Sorry, I overlooked your question. It's a teleflex tach, I also tried 3 other used tachs. i will quick playig with junk and just buy a new tach

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Thanks Paul...

I am a firm believer in using a tach that is the same manufacturer as the motor.
In your case, I would buy a Honda tach.....
I just visited the Honda site and they do list Teleflex gauges as one of their accessories....

I would buy what Honda recommends for your motor

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Tom, maybe it was a Ballistic prop I had originally on the boat

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About 2 years ago we repowered A Little Madness w/a Honda BF90D (I know it's not the same but I'll get to the point soon). On the advice of the Honda Regional Rep (not the mechanic) we installed a Honda Titan Solas 13 1/4 15R Stainless Steel Prop. The boat comes out of the hole like a shot and runs as fast as I could possibly want it for my wife & I. And before anyone asks, I've not kept any records having gone thru 2 back operations this year. I did get a new Honda instrumentation package in the purchase and agree on keeping it in the engine family.

The real point of my response is that these Regional Reps really know their boats and are best suited to get the right prop on your 75.

You can see our beauty on our personal page.

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I installed a new tach, put the 13.5x15 prop back on the motor and borrowed a gps. Turned 5600 rpm's @ 34 mph, I'm pretty happy with it. What do yall think?

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sounds like your right on. 5600 is the middle of the range. I would stick with it.

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Insted of starting a new thread I thought I would ask my question on this thread. I have a 2005 Honda BF75A outboard that has a 3X13.25X17 prop and I am only able to get 5,000 rpm at WOT with a speed of 29-30 MPH. I boat at Lake Tahoe with a surface elevation of 6,223'. What pitch would allow me to achieve 5,500 RPM. I would like to thank you in advance for any help.

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Eastport3338,

Paul is running a 15 pitch prop to get the 5600 RPM's at WOT...

You may never achieve his exact statistics as he is at Sea Level and you are above 6,000 feet but I would definitely try the 15 pitch and see how it works for you.

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Eastport3338,

You will need to drop to a 15" pitch prop to get your BF75 to 5500 RPM.

Your 75 HP outboard is only putting out 60-65 HP at that altitude, so 29-30 MPH is pretty good.

To discuss the special accommodations of outboards used at altitude, please start a new thread; it is usually better to start a new thread than to piggyback on an old (and very long) one.