Planing? Prop? Performance? Help!

[ckone0814]

Re: Planing? Prop? Performance? Help!

edumacate me a little...

A 13x17 prop has a 13" diameter and 17" of pitch - meaning it will theoretically advance 17" in one revolution, right? So if tech says "you could try a 15" he's speaking diameter, right again? If so, then the pitch of the 15 he's referencing wouldn't be 17, it would be higher, correct?

Would it be out of the question to ask them if we could try a 15? Maybe they'd be sitting on a used one we could throw on?

Thanks again everyone.

 

[MikDee]

Re: Planing? Prop? Performance? Help!

Let's make this simple...plz post a pic of your boat with the motor all the way down. Try to get a straight on shot that show's just how far below your prop is under the hull.

I assume your have power trim..

I see you do have power trim. Aside from dragging your trailer, or an anchor along with you something doesn't sound right here. Before you go buying trim tabs, please do as Tailgunner, & I suggested, and put up some pics of your setup, so we can take a look, and possibly nip this problem in the bud.

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

boats are generally sold with the lowest horse power motor for pricing purposes. At 3500 lbs that is a lot of boat for a 115 hp. I've got a 1972 SRV 180 which weighs 1800 lbs and I am running a 120 which is the lowest rating for that boat. I plane fine, but I also have smart tabs. most likely traded in because it was not enough motor for the last owner. The fact that it planed with two in the front tells me smart tabs will help, but you will still be under powered.

thanks FR. I'm starting to come to the same conclusion....

 

[freddyray21]

Re: Planing? Prop? Performance? Help!

edumacate me a little...

A 13x17 prop has a 13" diameter and 17" of pitch - meaning it will theoretically advance 17" in one revolution, right? So if tech says "you could try a 15" he's speaking diameter, right again? If so, then the pitch of the 15 he's referencing wouldn't be 17, it would be higher, correct?

Would it be out of the question to ask them if we could try a 15? Maybe they'd be sitting on a used one we could throw on?

Thanks again everyone.

he saying try a 15 pitch prop not diameter. by going down in pitch you get more power for a hole shot.

 

[MikDee]

Re: Planing? Prop? Performance? Help!

edumacate me a little...

A 13x17 prop has a 13" diameter and 17" of pitch - meaning it will theoretically advance 17" in one revolution, right? So if tech says "you could try a 15" he's speaking diameter, right again? If so, then the pitch of the 15 he's referencing wouldn't be 17, it would be higher, correct?

Would it be out of the question to ask them if we could try a 15? Maybe they'd be sitting on a used one we could throw on?

Thanks again everyone.

Usually they don't mean diameter if they mention a number like 15", they mean pitch, but that would raise your WOT rpm possibly out of the recommended range. True, a 13" Diam. prop sounds a little small for the weight of your boat, but I think you would notice slip (cavitation) if it wasn't doing the job. We need pictures, pictures, pictures

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

I will try to get the pics and info asap.

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

Just a quick question is the cavitation plate (the plate just above the prop) flush with the bottom of the boat?

Cavitation plate is = with the bottom of hull. I'll post some pics later.

 

[MikDee]

Re: Planing? Prop? Performance? Help!

Cavitation plate is = with the bottom of hull. I'll post some pics later.

Thanks, then maybe you do need a bigger diameter prop? but that also means less pitch, so you can spin it to the same rpm or a bit more,,, I see 6100rpm is the target according to the charts.

My old 24' SeaRay, I had to put a larger diam. 15"X17" pitch Michigan prop on it, make it easier to stay on plane, and to keep it from coming off plane in the turns, but that was a 4000lb I/O boat.
Maybe a 14" diam X 15" pitch prop may work for you?

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

Thanks, then maybe you do need a bigger diameter prop? but that also means less pitch, so you can spin it to the same rpm or a bit more,,, I see 6100rpm is the target according to the charts.

Maybe a 14" diam X 15" pitch prop may work for you?

Thanks. hwsiii wrote earlier, "If you happen to be using the 13" x 17" Painted steel semi cleaver prop, that could be a problem as that prop is designed to run real close to the suface of the water and it has veryyy litlle blade surface area and has some bow lift in it. What you need is a stern lift prop, not a bow lift with all that weight in the stern as well as if you are using the semi cleaver you need much more surface area to make that boat come out of the hole with that weight."

So putting together what you wrote and what hwsiii wrote are you each taking the same thing?

Probably apples v oranges but the 150 on my boat is fitted with "Performance Series" 14-1/4 x 18

 

[MikDee]

Re: Planing? Prop? Performance? Help!

Thanks. So putting together what you wrote and what hwsiii wrote are you each taking the same thing?

Probably apples v oranges but the 150 on my boat is fitted with "Performance Series" 14-1/4 x 18

Yes, I would surmise, the diameter sounds right, but you need to drop to a 15" pitch at least (maybe even less pitch?), to be able to recover RPM lost due to the extra load of a larger diameter prop. This is the right move, but Sadly, it's a trial, & error, process.

One more thing, I don't think this is possible, but maybe probable? Most outboards have a thru hub prop exhaust, just look in, & check to make sure there's nothing unusual obstructing that?

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

she's at the local shop now.

thanks for all the help.

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

pics attached

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

a few more...

 

[Tail_Gunner]

Re: Planing? Prop? Performance? Help!

If you have power trim heres a few ideals...

http://www.boat-props.com/Yamaha/11...s/411/?**********=394415353&*******=800117805

See those two ss 15p michigan wheels...those would be my choice the appollo more specfically. Second would be tabs..actually both. Is a 115 to little for that boat not if your happy with it. If you do have power trim dont take it for granted that triming all the way in will give you the best launch.."play a litte bit you might be surprised."

That is a heavy boat maybe but looks fun...WH rated those props as very good pushers and that's what you need.

http://forums.iboats.com/showthread.php?t=218877

#2. Apollo 19P Large blade....0-30mph 2.9 sec 0-50 7.9 secs. Top speed 52.6 5910RPM 11.1% slip

Final placing....
MWC Apollo 19P large-blade

0-30mph..........4-way tie as the second quickest in acceleration.
0-50mph..........4-way tie as well, but number 4 to 50mph...not bad considering the props tested
Top speed.........Only 1.8mph slower than the fastest 19P tested
Ave. slip ratio........10.74%, #3 in comparison to all 19P's tested.

MWC 013052 15X15 6550 42.1 PUSHES 800LBS OF SAND BAGS LIKE THEY ARE FILLED WITH AIR


http://www.boat-props.com/Yamaha/11...16834/?**********=394415353&*******=800117805

I believe I-Boats has a special on Nauticas tabs right now..yep..

http://www.iboats.com/Factory_Blemi...5753071--**********.020428943--view_id.486634

You may want to post for Nautijohn in Generally asked question's on just what tabs to use but those above should work..Id problably start there but the all of the above would make you grin im sure.

Stickly a opinion your milage may vary.

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

TG - thanks for all the information and the specifics. Assuming the motor checks out, this sounds like a good plan. I will be posting on Smart Tabs in "General" as you suggested.

Anyone else care to weigh in?

 

[Jdeagro]

Re: Planing? Prop? Performance? Help!

Ckone;

I am flattered that you asked me to jump in here (from another post), and I would like to tell you that the performance issue is simply the need for trim tabs. However, after reading all of the postings, I go back to the Yamaha test of a similar boat that had very different results. It does not sound like the HP to weight ratio is the problem either, not that it wouldn't do a bit better with more HP, but your problem is bigger. It sounds like you are not getting enough HP to the prop. It could be that the prop is incorrect (which may not be the issue either since the Yamaha test was with the same prop.

The simple test would be to try a different prop, the same as used in the Yamaha test. This will tell you quickly if the prop is OK, and will tell you in a few seconds of operation. If the performance mimics the Yamaha test then your in business. If changing the prop does not produce any better results then you have an engine issue. I am not going to recommend a larger engine as this does not address the problem with the engine you have, and it could be very satisfactory if running correctly. I am also assuming that the weight of the boat is similar (within a few hundred lbs.)

Remember that stepping up from a 115 HP to a 150 HP does not give you the extra 35 HP where you need it (at 2500 RPMs) since the additional HP is only developed completely at the higher RPM range (about 5500 RPMs). You will only get about 15 to 17 HP to use when trying to get on plane. Your problem is bigger than that. And my guess is that you could make that boat plane with a 90 HP, although it would be a strain.

Process of elimination (in order of priority and simplicity):

1) Try a different prop of the same size as used in the Yamaha test.
2) Get the engine checked by the Yamaha authorized Dealer, and Call the factory to involve a tech representative if necessary.

Once the problem is identified then move forward to fine tuning the performance.

There is no doubt that trim tabs (Smart Tabs or helm controlled Tabs) will improve the performance, ride , handling etc, but lets not hide the problem. Fix it first, then make it even better!

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

1) Try a different prop of the same size as used in the Yamaha test.
2) Get the engine checked by the Yamaha authorized Dealer, and Call the factory to involve a tech representative if necessary.

Once the problem is identified then move forward to fine tuning the performance.

There is no doubt that trim tabs (Smart Tabs or helm controlled Tabs) will improve the performance, ride , handling etc, but lets not hide the problem. Fix it first, then make it even better!

Thanks for the sound and frank advice.

She's currently at the local Yamaha dealer where it will be getting a full look w/ compression, etc. After that we'll be stopping at the local scale to make sure the weight falls within expectations.

I'm pretty sure the prop on her now IS the same prop as in the Yamaha test "13X17 black steel". The test was done in 07 and best I can tell, everything between the test boat and ours is the same except for what I would expect is a small weight variation.

 

[MikDee]

Re: Planing? Prop? Performance? Help!

I have previously, given you my opinion on a prop choice and,
Thanks for the pics, but I'm confused, it looks like there is some type of "notch", "tunnel", in the bottom just before the prop, that might be causing some type of turbulence when you try to get on plane? I wonder if your cavitation plate needs to be flush with the top of that tunnel, or notch?
But, that don't seem right either, hence my confusion

Water is naturally going to fill in that tunnel, and flow over your cavitation plate at low speed, and as you try to plane, creating a problem IMO, but once you're on plane, the tunnel would be out of the water,,, I think?

But, having that trailing edge of the tunnel so far ahead of the prop, means that the flow of water will rise some from there as you're on plane (as normally happens from the trailing edge of any boat), that might be restricting flow, causing too much going over your cavitation plate, creating a restriction unless you raise the motor up some.

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

Yes, there is a small cutout at the very back of the hull. the V stops about 6 inches short of the transom and the cutout starts. The transom plug is on the face of the cutout.

 

[ckone0814]

Re: Planing? Prop? Performance? Help!

Yes, there is a small cutout at the very back of the hull. the V stops about 6 inches short of the transom and the cutout starts. The transom plug is on the face of the cutout.

if the v of the hull ran all the way to the transom the cavitation plate would align with it. there is sort of an empty space there.