Planing question

[767Captain]

Never had this issue with our tournament ski boats but: our 23' walkaround fishing boat need the tabs down to get on plane. Boat weighs probably 4600-5000 lb loaded up. Has a 200hp outboard (single). Tops out around 41 mph. Won't plane, or takes extremely long to get on plane unless the trim tabs are down. Being new to outboard boating, I'm trimming the motor pretty much down, and setting the tabs down as well. Then it planes OK. Once on the step, I can raise the tabs & trim up the engine for speed / efficiency.

Am I doing this incorrectly, or do these outboards really need the tabs to get up?

 

[roscoe]

Re: Planing question

Sounds like you are doing it right.

More experienced people out there with this type of boat, but in my opinion, it is not the outboard that causes the problem.

More so the prop, motor mounting height, and only 200 hp.
What are your wide open throttle rpm's?

 

[dingbat]

Re: Planing question

First off, what hull are we talking about? Hulls make a big difference in the way a boat performs. What prop are you spinning?

From the sounds of it you?re propped for speed. Good if you like to go fast but it takes the kick right out of your lower end.

Here are my numbers:
My normal load around 5,300 lbs. I?m pushing it with a 200hp Ocean Pro with a 14" x 17", 4 blade, Renegade Offshore prop. At WOT running 35.4 kts @5600RPM.

The hole shot on this boat will pin you in the seat. No problem whatsoever getting up on plane, tabs or not.

 

[ziggy]

Re: Planing question

I'm trimming the motor pretty much down, and setting the tabs down as well. Then it planes OK. Once on the step, I can raise the tabs & trim up the engine for speed / efficiency.

Am I doing this incorrectly, or do these outboards really need the tabs to get up?

sounds right to me. but maybe put the engine trimmed all the way down. if that isn't satisfying. then go for the prop. less pitch for better hole shot or maybe 4 blade prop. yes, you'll likely loose top end speed...

are you able to achieve wot spec for your engine with the prop you have? if not. something needs to change (like the prop) so you are in the right rpm range. this is critical to be in the proper wot spec range...

 

[a70eliminator]

Re: Planing question

I have to agree that it's a prop issue, 40 knots is good for that size boat and 200hp, trouble getting on plane yet good top speed?

 

[Texasmark]

Re: Planing question

I'll go with the xperts.

200 hp on a 23' @ 5klbs and 40k (45mph) top end.....I think you need to decide which you prefer....hole shot or your top end; usually can't have both.

Lower pitch and more blades would help your hole with your tuck in and down tabs that you currently do, but you will loose that 40k on the top end and personally, I don't know anyone that can REALLY stomach less top end. Grin.

Mark

 

[767Captain]

Re: Planing question

Great, thank you. I was hoping it wasn't operator technique... The boat is turning good rpm, I think around 5600-5900. The hull is a Wellcraft 23 Excel offshore walkaround, 21 degree deadrise. I am used to the solid grunt of an inboard direct drive tournament ski boat. I would gladly trade top speed for hole shot for our usage. The boat has a 15 X 17 prop on it now. 17 is the pitch measurement, right? In the boat's original manual, it specifies a 14.5 X 19" three blade prop. Wouldn't that increase pitch and top end, while further hurting hole shot? Do I need a 15 or 16" pitch prop?

 

[dingbat]

Re: Planing question

Loaded up your boat is probably another 800 - 1000 lbs heavier than you give it credit for.

A coastal boat without a good solid low end to get you out of the hole is a dog. If it?s an aluminum prop go to stainless. If it?s stainless prop go to a 4 blade Stainless. Put a 14?x17? 4 blade on it and play with the motor height if need be.

 

[high'n'dry]

Re: Planing question

Put a Mercury Revolution 4 on it in a 17 inch pitch. This is a efficient, fast, prop with a lot of stern lift and tons of traction.

Your ski boats are not a good comparison to a deep V coastal boat.

 

[Texasmark]

Re: Planing question

Like Hi and Dry said, material makes a big difference and Aluinum vs SS is night and day. BTDT

The difference in the props you mentioned are such that the former is designed to run at a higher boat speed with lighter weight than the latter. Higher speeds use higher pitches and smaller diameters....get better prop effeciency at the higher speeds. The converse (lower pitch and larger diameter) is for pushing, like pushing you out of the hole, and subsequently they are not as efficient at high speeds so you sacrifice some top end.

More blades help you to grab more water while pushing, but at high speeds they tend to get tangled up with one another and loose thrust due to turbulence caused by the previous blade which is closer, due to the number of blades. Walleyehed is the prop expert.

I like dingbat's answer. He is real close to where you are, with minor hull , trim and load variations. His prop fits well against where you currently are and his performance numbers are what I was talking about. Sounds to me like his prop brand-material-blade number/pitch-diameter is a great starting point.

Mark

 

[767Captain]

Re: Planing question

I need to find a place around here that would let me test drive a couple props. The current prop is an SST stainless steel 15 X 17 three blade. I guess I could try a 14 X 17 four blade. Wouldn't the pitch be the same though? Cavitation plate is right about level with the hull bottom. Regardless, I really love this boat, what a great configuration.

 

[high'n'dry]

Re: Planing question

I need to find a place around here that would let me test drive a couple props. The current prop is an SST stainless steel 15 X 17 three blade. I guess I could try a 14 X 17 four blade. Wouldn't the pitch be the same though? Cavitation plate is right about level with the hull bottom. Regardless, I really love this boat, what a great configuration.

The prop you are running is a poor choice for that boat. As well, it is not simply the number of blades but the design of the prop. The Merc Revolution 4 is a known good performer for exactly that type of circumstance. It has tremendous stern lift. Very few props including other four blades are in the same class of performance, traction and lift. I would not go down in pitch with the Rev 4.

 

[767Captain]

Re: Planing question

Pardon my ignorance dealing with outboards, but can an Evinrude accept a Mercury prop? Special adapter?

 

[NSBCraig]

Re: Planing question

That's what the tabs are there for.
Play with it till you get good at it.
Change props will lose you top speed and lower your cruise speed too.
You said it's a stepped hull, your boat is made to use tabs.
Don't re prop learn to drive the boat.

 

[high'n'dry]

Re: Planing question

Yes, there should be hub kits available. A stern lifting prop like the Rev 4 is a completely different animal from the prop you have now.

 

[767Captain]

Re: Planing question

Thanks for the advice so far. Ran the boat today, wide open. Top speed (GPS) approx 40.5-41 MPH. Max RPM 5200. I believe this engine should turn about 5800-6000 max rpm?

 

[jay_merrill]

Re: Planing question

Thanks for the advice so far. Ran the boat today, wide open. Top speed (GPS) approx 40.5-41 MPH. Max RPM 5200. I believe this engine should turn about 5800-6000 max rpm?

There's your problem - you have too much pitch on the prop. WOT rpm is how you figure out if you have the right pitch or not. My guess is that Dingbat is exactly right. Your typical operating weight is probably more than you think it is.

The idea is to keep WOT rpm within the acceptable range, as defined by the manufacturer. That range on your motor is probably (double check this at the dealer) 5,000 - 6,000. If you are only getting 5,200 at WOT, you are at the bottom of the acceptable range and are lugging the engine. My guess is that you are going to have to drop to at least a 17" pitch prop, regardless of material, number of blades, etc.

Think of this as an old pickup truck with a busted, 3 speed tranny - in our hypothetical, you only have 3rd gear (19") to work with and that isn't working well as a starting gear. If you had 2nd (17"), you'd still have more gear than you'd really like, but it would work better.

Since boat props are always fixed (with a few exceptions that never seemed to work very well), there are always compromises to be made. You want enough pitch to move the boat at a decent speed, but not so much that you have poor "hole shot." You can compare this to the light aircraft that you learned to fly in, before you graduated to one with a constant speed prop.

Generally speaking, for each 2" change in pitch, you will see a 400 rpm difference at WOT. This is not an absolute - prop material and design can affect it - but its not a bad rule of thumb. If you go down two inches in pitch, you will most likely pick up about 400 rpm. That puts you at 5,600 WOT rpm, which will be a big improvement. Combine that with shedding a little unnecssary weight in the boat and you might get up to 5,700 or 5,800 WOT rpm.

"Kick the tires and light the fires - it time to do some yankin' and bankin'! No wait! You can't do that in a 76!"



???

 

[TexMojo]

Re: Planing question

I'm am def not an expert, but I am pretty sure I read somewhere that trim tabs are not to be used to get on plane, only to offset chop. I think it mentioned trimming them down to get on plane puts stress on the engine. could be wrong.

 

[dingbat]

Re: Planing question

Thanks for the advice so far. Ran the boat today, wide open. Top speed (GPS) approx 40.5-41 MPH. Max RPM 5200. I believe this engine should turn about 5800-6000 max rpm?

From the manual.
Full throttle operating range: 5000 to 6000 RPM
Minimum RPM: 5000 RPM
Peak Horsepower: 5500 RPM

Mine is propped @ 5450 RPM. Pretty much right at peak HP. Anything above that on your on the down hill side of the HP curve.

 

[180shabah]

Re: Planing question

Your ski boats are not a good comparison to a deep V coastal boat.

I was wondering when someone was going to catch that. He is comparing a vette to 1 ton pickup here. The only valid comparison between the two boats = they both float.

I am pretty sure I read somewhere that trim tabs are not to be used to get on plane, only to offset chop. I think it mentioned trimming them down to get on plane puts stress on the engine. could be wrong.

Wherever you read that, never read there again. Tabs are the best way to get a heavy, underpowered or deep v hull up ontop of the water.
They also work to level you ride and lower you planing speed in rough water.