Prop Selection- Now with Tach!

[java230]

Re: Prop Selection- Now with Tach!

Yep close enough for this old boat. I'd guess the recommended 11 pitch would have put it right in the WOT sweet spot.
I really appreciate the help I got here!

I'll get the loaded ( well no niece this weekend) and light load data this weekend! Headed to camp on the lake again.

 

[java230]

Re: Prop Selection- Now with Tach!

Ok data from this weekend:

Loaded: 200lbs of dog, one cooler, wife, myself, duaghter and niece. Id estimate it 750lbs of live stuff, 40 lbs of anchor, fall gas tank (6gal).
WOT max was 21.1 MPH @ 4350 RPM's. Averaged 20.5. Way better! Before i could only manage 9.9 with the 14" pitch.

Light load: me, full tank of gas, anchor gear. 27.3 MPH at about 4850 RPM's. Was going great for about 2-3 mins before it fouled the plugs. Seemed happy at 4300 like the above cruise, which pushed me at 25ish with no more fouling.

Seems like it might be running a bit rich at WOT. But either way i am way happier with this prop. Just for a reminder its a 10" 12"pitch cabelas stainless with a brass hub.

 

[dazk14]

Re: Prop Selection- Now with Tach!

I'm glad you can plane with your heavy load.

Just an fyi, there is rubber between the brass and the stainless prop.

FWIW, the prop you have is a much different animal than a basic aluminum and tend to act an 1" bigger in pitch.

The thin blades and progressive pitch design are likely making it work here.

If the motor cut out while running WOT that is normally a too lean situation. I wasn't there, so I can't be certain.

A check of the plugs, would give you a definitive answer.

When you have time, you should clean the carbs and verify float height. In the meantime, you're wise not to push it.

 

[java230]

Re: Prop Selection- Now with Tach!

I'm glad you can plane with your heavy load.

Just an fyi, there is rubber between the brass and the stainless prop.

FWIW, the prop you have is a much different animal than a basic aluminum and tend to act an 1" bigger in pitch.

The thin blades and progressive pitch design are likely making it work here.

If the motor cut out while running WOT that is normally a too lean situation. I wasn't there, so I can't be certain.

A check of the plugs, would give you a definitive answer.

When you have time, you should clean the carbs and verify float height. In the meantime, you're wise not to push it.

I'm thinking it was fouled plugs, luckily I had a new set on board and changed them and it started right up again. They had lots of oil and some chunks of oily looking gum/gunk. It will probably get a full rebuild this winter.

Still think it was leaning out with the plug description?

 

[java230]

Figured I could update this. Been using the boat a ton with the new prop, so I have some decent data now.

With 600lbs of people food etc it runs 25-25.5 MPH on the GPS with light chop, at 4680 rpms. With just me its ~27, but the tach is jumpy. Mark's Marine prop slip calculator puts me at 5.2%. I haven't touched the motor other than replacing the poppet valve gasket and the water jacket gasket, and the powerhead to lower unit gaskets. The carb probably could still use a rebuild, but I broke so many bolts doing those gaskets I haven't wanted to touch it again.

 

[Silvertip]

I also feel something other than prop is amiss.
1) Verify that the tach is reading correctly. If it's not right you only spend money chasing a whim
2) Is the engine making full power? The average Joe rarely knows that and in fact many people can't tell when one cylinder on a multi-cylinder engine is dead.
3) Is the throttle opening the carb butterflies fully at WOT?

One reason I suggest engine/tach issues is that a 40 HP Merc with a 1.83 gear case almost always has a 10-1/2 x 13P prop on a planning hull. With a 2.0 gearcase a 14P in similar diameter the engine should should not be lugging as seriously as yours. At this point do not spend money on props until you verify engine & tach performance.

 

[java230]

I also feel something other than prop is amiss.
1) Verify that the tach is reading correctly. If it's not right you only spend money chasing a whim
2) Is the engine making full power? The average Joe rarely knows that and in fact many people can't tell when one cylinder on a multi-cylinder engine is dead.
3) Is the throttle opening the carb butterflies fully at WOT?

One reason I suggest engine/tach issues is that a 40 HP Merc with a 1.83 gear case almost always has a 10-1/2 x 13P prop on a planning hull. With a 2.0 gearcase a 14P in similar diameter the engine should should not be lugging as seriously as yours. At this point do not spend money on props until you verify engine & tach performance.

Thanks for the reply. Honestly its an old engine, Im sure its not making what it used to.

1) tach appears correct to my moderately skilled eye. idle was on spec (iirc) ill take a peek next time im out. The tach reading does bounce a bit when im alone and it revs beyond ~4800. Its an induction tach.
2) I do believe its running on both cyls, the plugs both appear to be the same, one is not oiled up. I have not tried pulling a plug wire.
3) Appears to. butterfly goes to parallel with the carb inlet, as close as my eye can see anyway, not obviously not fully open.

 

[dazk14]

It's great to hear everything is going well and a great picture! Most importantly, your using it and not "sweating it"!

FWIW....If you're bored and just need something to work on...

The tach. Ensure it's on the lower cylinder and routed away from the other wire. You may need to separate the 2 plug wires if they cross or are close, to minimize an errant signal... but you really only need it once to get the motor/prop setup. Then it's more of a toy if you have a gps occasionally.

When running at the lower end of the rpm range... more (often) decarbing is needed.

The low slip (5.2%) is due to using 12" pitch in the calculator as opposed to 13" which is how a cupped prop acts. It is also progressively pitched, so the pitch changes across the entire blade face, so results are merely a ballpark.

You can gain a bit more, and plane easier if you want to move the motor up on the transom. If it's bolted on the bottom (which it should), it can be a PIA. I can't recall whether you have a slot in bottom holes, which would give a bit of height. That prop will have plenty of bite for raising.

And of course, if you come across a nice 11" stainless prop for $50 bucks...well you already know what to do.lol

The carb nuts usually come off fairly easily. If you don't like how they look, pre-spray a few times with your favorite penetrating oil. Aero-Kroil is what we've switched over to in the shop for a few years now.

 

[java230]

It's great to hear everything is going well and a great picture! Most importantly, your using it and not "sweating it"!

FWIW....If you're bored and just need something to work on...

The tach. Ensure it's on the lower cylinder and routed away from the other wire. You may need to separate the 2 plug wires if they cross or are close, to minimize an errant signal... but you really only need it once to get the motor/prop setup. Then it's more of a toy if you have a gps occasionally.

When running at the lower end of the rpm range... more (often) decarbing is needed.

The low slip (5.2%) is due to using 12" pitch in the calculator as opposed to 13" which is how a cupped prop acts. It is also progressively pitched, so the pitch changes across the entire blade face, so results are merely a ballpark.

You can gain a bit more, and plane easier if you want to move the motor up on the transom. If it's bolted on the bottom (which it should), it can be a PIA. I can't recall whether you have a slot in bottom holes, which would give a bit of height. That prop will have plenty of bite for raising.

And of course, if you come across a nice 11" stainless prop for $50 bucks...well you already know what to do.lol

The carb nuts usually come off fairly easily. If you don't like how they look, pre-spray a few times with your favorite penetrating oil. Aero-Kroil is what we've switched over to in the shop for a few years now.

I may play with the tach. It was hard to keep it away from other stuff and still find a way out of the cowling. It settles at 4680-4660 at WOT on cruise. Just jumps a bit getting there.

Motor is bolted in a single hole in the bottom. Not wanting to deal with moving it. The AV plate is only about 3/4" below the keel on the hull anyway. (iirc, its been awhile since I stuck the level on there!)

Yeah I just had a nightmare on the water jacket cover bolts. Broke every one..... Its been a salt motor. That was after a couple days of PB soaking.

 

[dazk14]

Your dialed in well, so enjoy.

Heat and a special socket adapter for an air chisel,saves 90% of the bolts we use to break.

It is a snap on tool, and most shops don't know it exists, so we're not advertising it.

PM me if you have an air compressor and air chisel (which can be a Chinese cheapo.