Performance numbers
 

Since it came up again in two more PM's this week, here are my performance numbers and info.

'72 Seafari 20' w/ 2006 Mercury 90 ELPT Optimax that weighs 376 lbs, transom mounted. Boat has Trinidad anti-fouling bottom paint, and is unrestored condition.

Currently turning a Quicksilver Trophy Plus 4 blade 13x21 SS prop, with a skeg-mounted hydro-shield. (I would be better off with 19" pitch)

WOT with 3 adults and full fuel is 5350 rpms at 34 mph in a light chop, burning 10.8 gph or 3.1 mpg. (I need to turn 5700 RPMS at WOT to be just right on the prop)

Cruise is 3900-4100 rpms at 23-25 mph, burning about 4.9 gph or about 5.1 mpg.

Minimum planing speed is 14 mph, but requires throttling up to 17 mph, and then falling back to 14.

Absolute Best Economy is 3800 RPMS at 22 mph and 5.3 mpg

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Those numbers look a lot like my old seafari 20, 150 merc from the 1970s, just a lot better fuel economy and slightly slower wot.

Mine had the same issue with low speed planing, like many boats. I've had two that did not, a 24 Seabird (24'deepV, 350 chevy, volvo duoprop) and my 25 Seafari with essentially the same power package. Both would plane solidly at about 12 knots. I always ascribed the low speed planing in these boats to the duoprop's low end torque, but maybe it was something else. Any opinion?

Re: Performance numbers
 

Connor,

I think low speed planing is all about weight distribution. My Seafari would plane at about 12 kts (with a Bahamas type load, including about 80 gallons of gas) with the 300 lb 115 hp V-4, a 13 3/4 x 15 SST prop, a Doelfin and trim tabs. On the Bahama trips I always had a lot of gear in the cabin including a couple of dive tanks in a rack I built aft of the head, the gas jugs were carried amidships, and I put a 60 qt cooler in the stepdown. I mounted pad eyes in the 4 corners of both the cockpit AND the cabin. I ran a web of lines between them to keep everything from shifting around in rough conditions, and I didn't put any heavy stuff in the aft area of the cockpit.

Current rig with a much heavier motor (+ 130 lbs) sitting 30" further aft on a bracket would not plane below about 18-19 kts, UNTIL I went to a 4 blade prop! A stern lifting prop makes a world of difference. It now planes easily at about 12 kts. I bet that Duoprop, with 2X the number of blades, creates a lot of stern lift. Both the Seabird and 25 Seafari have so much deadrise that I would think they would struggle at low speed without a good stern-lifting prop. Denny

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Must be the stern lifting prop. We dove very heavy in the 20 seafari, 10 tanks in the boat, 7-8 of them forward, and the boat still did not want to plane slow. In the other boats, weight distribution did not seem to matter much.

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Denny, I think you also have to take into account the engine's power curve and the propping. Granted, a tail heavy boat won't like planing at low speeds, but if you're running a big two stroke that needs to run at low rpms at 12-15 kts, the engine may bog and drop you off plane if it's not propped right. I reduced the minimum planing speed on my 20 SF considerably by going to a 17P Mirage. The combination of lower pitch and stern lift made the difference. I suspect Connor's Duoprop, with very low slip, is making the difference for him at low speeds. I should be able to offer a comparison when I launch my 25 with a Bravo I drive.
Dave

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Dave, That's a good point about the engine's torque curve and where you're operating on it. Probably makes a good argument for running a smaller engine also, at least with a 2 stroke outboard! With my old 115 I was running a 15" pitch SST prop and it was turning about 3200-3500 at min planing speed, so it was making fairly decent torque. I normally cruised at 20 kts @ 4500, but on one trip with following seas, it started falling off plane when going "uphill", so I punched it up to 4600-4700 and then it would stay on plane with no problem! I later put some marks on the throttle quadrant and then had someone move the throttle while I watched the linkage on the motor. What I discovered was that up to about 4500 rpm, the linkage went to full spark advance, but the throttle butterflies only moved about 10-15 degrees! During the last 30 degrees of "power lever" movement, the throttle butterflies opened almost 90 degrees! The motor also got a lot louder and was obviously developing a lot more power. (Visualize the sound of a toilet flushing with the sound of the gas pouring thru all 4 wide open barrels of the carbs! :D) Denny

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Yeah Denny!! We all know what that sounds like and it's now at a smooth $4+ per gallon!! :rolleyes:

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Fr. Frank

Can you suggest a prop for my 20 foot M.A.? I just bought a 2000 Yamaha F100 (F90) which I read is the same as a 4 stroke Merc 90. I think the prop splines are interchangeable. It is ~356 lb dry. I have been looking at 4 blade Solas props, or Craigslist, but I am not sure on pitch. I have a lightish kicker (58 lb) on the stern and am more concerned with being able to play in the rough stuff than go fast, so response to throttle is key. Is a 4 blade 17" prop too little pitch?

Re: Performance numbers
 

2000 Yamadog F100: 2.31:1 gear ratio, Max of max rpm is 6000.

Assuming you're getting a true 100 hp, then you probably need a 13.75"D x 19"P, or a 13.5"D x 17"P to be able to turn 6000 rpms fully loaded (or close to it). You should have a top speed in the 32-35 mph range. I would try to start with a 19"P prop.

Rremember: More pitch = less rpms. You could get by with a 13.25"x20"P or maybe even a 13.25"x21"P, but the Yamaha F100 is NOT known to be a torquey motor.

Re: Performance numbers
 

Props confuse me
A 13.75 x 19 or a 13.5 x17? The second is less RPM and less pitch than the first. Maybe this is the range you think I will be in?

There is a 4 blase SS Yamaha 13.75 x 18 for sale locally. $275 asking price. Not sure if it will fit my gearcase. It fits the F150.

Also, how do you like the hydroshield?

Re: Performance numbers
 

Yes, I think you'll be in the 17" to 19" pitch range on your prop. However, there is absolutely no substitute for trying out a prop. I don't know if the 18" you mention will fit your gearcase or not.

The 19"P prop will turn less rpms than the 17"P.

As to the architecture, generally speaking, the greater the pitch of a prop, the smaller the diameter. A 13.5"D x 19"P propeller is 13 and a half inches in rotating diameter, and without slippage moves a theoretical column of water 19 inches long with each rotation; i.e.; twisting it one complete rotation in a block of gelatin would cause it to move 19 inches.

Because of the greater number of blades effecting water moving, the effective pitch of a four-blade is greater than a 3 blade. In other words to maintain applied torque when changing from a 3-blade to a 4-blade prop, you usually need to reduce the pitch by 2 inches. A motor that turns a 19"P 3-blade to max of max at max will not be able to turn a 19"P 4-blade to the same point, but would need to drop to a 17"P in a 4-blade. There are some very important variable that can change all of that, but generally speaking, that's the way it works.

As for the HydroShield, I cannot speak highly enough about it.
I have no trim tabs, and prior to installing the HydroShield, I would fall off plane at about 19-20 mph, and took 6-7 seconds to plane with my current 90 hp Optimax.

WITH the HydroShield I can stay on plane down to about 14-15 mph, and I get on plane in about 4-5 seconds. The boat is also more responsive to changes in thrust trim, enabling a much softer ride in a chop.

This is the 3rd motor I have put a HydroShield on. I really love it, AND it protects my prop and skeg in shallow water, which I frequent.

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Thanks for the explanation! One more question. Which size hydro-shield do you run (or recommend?)

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Onward Christian Soldier! And Happy Easter! Nice clarification on propping - that should help fishstretcher and others, imensly... but screw the prop - we know you're really trying to protect the manatee with the hydro shield :D :D :D

How they say - It's all good! ;)

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I run a medium sized HydroShield on my 90. I used to run a large on my V6 Mercury, and I ran a medium on my 115 Mercury I6.

And no, Gillie, I don't think these things would protect a manatee. Most manatee traumatic injuries and deaths are not caused by being cut by the prop, but by being struck by the lower unit, breaking bones and even spines. It's like hitting a manatee with a 4000 lb club traveling 30-50 mph. That's why they have the speed zones, instead of just requiring propeller cages.

When I was a kid, I swam with and played with manatees almost every week. My brother and I were two of the kids filmed by Philippe Cousteau swimming with and scrubbing manatees by the boat locks in the Palm Beach Canal, between Lake Worth and West Palm Beach, FL, back in the 60's. If you scrubbed their bellies with a stout scrub brush, they would let you ride them for while :)

There used to be a marina there between Dixie and Federal/Olive highways called Lake Worth Yacht Basin, of which my grandfather was part-owner. Back then both the Dixie and Federal bridges were drawbridges.

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$110 plus shipping is about 2x-3x a Doelfin. Maybe dealers have them cheaper...

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last time I bought one was in '06, from a marina, and it cost me $65. And Doelfin won't protect your prop and skeg.

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I have been calling around, and found Maritime Solutions wasn't that interested in customer service ( I won't stay on hold forever). The main # at hydro-shield didn't seem to go anywhere. Do you recall who you bought yours from?

By the way, based on your advice, I got a Solas 12-3/4" x 17P 4 blade "Amita" prop for the stern lift and relatively shallow pitch for my F100.

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I bought my last one at Magic Manatee Marina in Homasassa Florida. 352-628-7334 Talk to Kent Mylin to see if they have them currently in stock.

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Thanks.

Kent at Magic Manatee marina very courteous, but they didn't have what I needed.

I eventually got in touch with hydro-shield via phone. They are experiencing the crap economy, so "Salon-Salon" is their retail outlet, FYI. I ordered one. I will report back when it shows up -it should ship "this week".

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It did ship, and on time. So it seems they are small time operators due to the economy, but I did get my order after they called back and took my order.

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Let me know how you like it!

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Well, I finally got a chance to test it.

I have a 20' Master Angler with a 100 HP "Yamadog" Yahmaha four stroke. I have a 4 blade 12-3/4 x 19 Amita aluminum prop by Solas.

I have the 2 batteries on the port side of the forward part of the center console. A 20 gallon aluminum tank is up there too. The center hull tank has been pulled and replaced with buoyancy foam.

In addition to the ~376 lb Yamaha F100, I have a 6 HP 25" shaft pull start Tohatsu SailPro with a 6" pitch prop as a kicker.on the starboard stern. It has a 3 gallon tank that sits in the center console.

So balance fore- aft isn't awful, but the weight at the stern is probably 430 lbs with no kicker. And with a starboard helm, that isn't great. But the transducer seems to help, maybe?

With the batteries and tanks forward, the deck drains are above water, perhaps by 1" at rest. With a stock deck.

On the maiden voyage, it pulled 5400-5500 RPM with a 2nd passenger for 28.0 kts before I ran our of river (maybe 200 yards between buoys). With a little under 400 lbs of passengers, perhaps 16 gallons of fuel, and 75 lbs of tools and another 50 of anchors and tackle.

With some practice tweaking the trim it might pull 30 knots if I can run for a few hundred yards. It planed down to 12 knots with improper trim, maybe a bit slower, even.

It has no problem getting and keeping the stern out of the water. I knew it wouldn't be fast, but in the channel chop I was outrunning any boat even close to my size. And the ride is amazing.

My single beef is the stiff feel of the Teleflex SAF-T-STEER no feedback unit. It is brand new.

I suspect I would have a higher top speed with less drag with a conventional foil, but would fall off plane faster with a cavitation late foil. I have the large size hydro-shield. It comes of plane very softly. It is quite nice.

It bogs out of the hole, as I was told to expect, but as bad as an older two stroke, and I rebuilt the carbs myself and haven't timed the throttle sensor or synced the throttle shutters yet. So there is a little more left in it yet to aid in power and holeshot, I think.

Thanks for the tip Fr. Frank!

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Sounds great! And trust me on this, you'll love the small fuel bill. I took my boat out July 4, with 5 adults on board, running at various speeds up 28 mph, but about half was no-wake speed of 5-6 mph. On the water for 9 hours, with about 1.5 hours where the motor was not running, including towing a disabled boat for about 2 miles. GPS says I covered 22.3 miles throughout the day. When I filled up the next day, I just managed to squeeze 3.2 gallons into the tank.

Yes. Absolutely true. I averaged 6.9 mpg through the course of the day. Beats the heck out of the old carb Merc XR4.

That F100 may be just as good on fuel.

Re: Performance numbers
 

I'm about 80% done with a rebuild on a '72 Seafari. (my 4th Seacraft, owned 3-23's over the years) I decided on a new Suzuki 140 for power as it seemed like a logical choice for this application.

Splashed it for the first time this week...propped it with a Suzuki 14 X 20 3 blade SS prop. Acheived 37K at 6200, so it's pretty spot on. Will post some fuel burn numbers as I record them in the future.

I placed the new 50 gallon fuel tank about 2 feet forward and changed the boat to a 25" notched transom, with the motor directly on the transom (no bracket).

The motor looks none too big and the boat sets fine in the water with the 421 Lb motor.

Looking forward to some great times and memories on her.

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congrats have fun

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Nice choices. Sounds like you've dialed her in. Enjoy the new power. Spot on, Mate. :cool:

Could you post some pics of your restoration. Look forward to hearing more on your performance #s.

Cheers.

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HeadHunter,

Congratulations and good luck with the new Seafari! Please post pictures if you have them. Look forward to seeing the speed / RPM / fuel consumption for the DF140. Heard nothing but good on the DF140. Great engine.

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I made a mistake I have a 12-3/4 x 17 4 blade, not 19" pitch.

Still tuning, about 29 kts/ 33MPH at 5500-5600 RPM. I haven't synced the carbs yet and I am not sure I get them wide open.

This hull is awesome out in the slop. I accidentally planed it straight out of the mouth of the Merrimac this week. It seemed a little rough going over the standing 4 foot waves at 18 knots! That stupidity would have swamped my other boat.

Other than when I was at WOT heading into a 10-15 kt breeze off the starboard bow, it was a super dry ride.

It would have been perfect if we caught fish and the 11 year old tilt/trim didn't quit (looks like worn brushes). But still better than a day at work.

:D

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An update: with this setup including some trolling and a run down Plum Island at WOT and back north at cruise, I did about 26-28 miles on 6-7 gallons of fuel, by the gauge. At WOT with the size large Hydroshield and a stern lift prop, I feel like I almost have too much lift at WOT, but just right at cruise which is about 20-22 knots/ 23-25 MPH.

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Sounds very good. You're describing between 4-5 mpg, at a very comfortable cruise. Here's a hint on limiting the effect of sternlift at WOT: Run the motor trimmed out/up as far as you can without losing thrust or ventilating.

I just raised my motor one hole and I am considering going to a 13.25 x 15P 4 blade Solas Amita 4 to see if I can redline my motor. I will know soon.

Let us know as soon as you have the data.

Will do. Java prop predicts 2-3% better efficiency. Hoping for 35MPH.

If I like the 15p, then I might finally go stainless. Maybe 3 blade, depending on how I feel about the amount of stern lift. I feel like the 15p in aluminum might be a little too little pitch, but I will have 2 weeks on the water after the 4th of July to A/B compare. I guess I should bolt on the paddle wheel for a test. GPS might not be accurate with wind and tide.

Raising the motor one hole got me a little. Maybe a knot of speed, but only if I trim the motor to a point where it starts to ventilate a bit, I think. When I did that, I could jump on the throttle and slip or ventilate to get to 5900 RPM occasionally.
But the extra speed came at the same 5600 RPMs, steady state, withou crazy trim- so that's good. And the cable steering is better (lighter). But I need a hydraulic helm.

I will check throttle adjustment tomorrow. If that is correct then I will bolt on the 15 pitch. If not, then I will adjust it then try a top speed run again.

Update- the 13 x 15 4 blade pulls to redline, and when trimmed the same (nearly blowing out in turns) is a few tenths of a knot faster before redline. Top speed is really splitting hairs. But it gets there a lot faster and it is a little less trim sensitive. I love the holeshot. Trolling is a little more adjustable, too.

9% slip calculated for this 13 x 15" pitch four blade prop at 6000 RPM at 29.3 knots over ground
15% slip for the 12.75 x 17" pitch 4 blade prop turning 5600 RPM at 29.1 knots over ground