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  Propeller: 70-HP Nissan, NAUSET 16

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Author Topic:   Propeller: 70-HP Nissan, NAUSET 16
SpeedBump posted 04-09-2004 10:34 PM ET (US)   Profile for SpeedBump   Send Email to SpeedBump  
I have a 70 HP Nissan turning a 14 1/2" X 17 pitch elephant ear aluminum prop on my 16'7" Nauset. Just had it out today for the first time this season. I have been very pleased with the overall performance of the engine but wonder if I have the proper size and pitch.

My top end today was 34.4 MPH by GPS and was turning 6,000 RPM as shown on the tach. I can run 30 MPH at 5,000 RPM. The engine is rated 5300-5600 RPM. The performance is good but I don't like to run at WOT for long lengths of time. Can I adjust up or down to get the same top end speed but at lower RPM? Would going SS in the same diameter and pitch gain me better performance?

Sal DiMercurio posted 04-09-2004 11:30 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Speed, it looks like your over reving by 400 rpms.
You most certainly can gp up 2" in pitch to a 19p which will pull your rpms down where they need to be, plus you might see if there is a smaller diameter for the engine.
I really don't see that engine needing a 14.50 diameter to hold that boat up.
I'm not familiar with your particular engine, but 14-1/2" diameter is bigger than the prop on my 200 hp & 20' boat, I just don't see you needing that much dia.
How high is your engine mounted ?....1st holes, 2nd holes ?????
I suspect you can run that engine on eith the 2nd or 3rd set of holes.
If your all the way down,. you will gain about 150 rpms with each hole going up.
The higher you mount the engine, the more rpms you will twist, & possibly might be able to go to a 21p if your now all the way down & raising the engine to the 3rd set of holes.
I say it's possible.
In order for the prop to not blow out, you would need a s/s performance prop if raised to the 3rd set of holes because a stock aluminum will break loose long before a s/s performance prop will.
Sal.
Sal DiMercurio posted 04-09-2004 11:37 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
If I'm not mistaken, you can run a 13.25 diameter prop on that engine.
I'm confident that your engine can twist a 13.25 x 19 or 21 Stiletto but you would need to have it re-hubbed from either a Johnson or Merc hub.
Sal
A Stiletto would make that boat ride complety different & it would hang on much better.
Sal
SpeedBump posted 04-10-2004 09:14 AM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Sal thanks for the feedback. The engine in mounted all the way down. It is bolted through the top holes and through the bottom blind hole. Haven't wanted to raise the engine because of the blind hole mounting issue and needing to redrill the transom to use the open lower holes. The cav plate is just above the drain hole on the transom so I am not that low in the water.

I was incorrect in my engine stats, the RPM range is 5150 -5850 max. Nissan does offer a V1900 and V2100 pitch prop but the higher pitch as I understand are for lighter loads. I usually have 3-4 people on board.

jimh posted 04-10-2004 10:13 AM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was "Proper prop size."]
SpeedBump posted 04-15-2004 08:48 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Sal D.- Boy was I off on my measurements. Rechecked the prop specs- Prop Diameter is 13 3/4" diam and a 17 pitch. Have ordered a 19 pitch Nissan aluminum prop by Tohatsu, it is supposed to drop my rpms by 350 RPM. Had inquired @ a cupped SS prop, was quoted $660. Was told by the dealer the Tohatsu aluminum prop is cupped and other that SS being a bit thinner it would not really out perform the Alum one. He stated Tohatsu is using Merc prop technology in its design.

I'll opt for the $160 aluminum instead. Hope to have it on the boat next weekend. I should get back into the 5600 RPM range WOT so to not cook the engine on long runs and pick up a few MPH to boot.

Salmon Tub posted 04-16-2004 07:36 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Hey SpeedBump, was wondering, are you running in water with any current, because the numbers seem off by a bit. I have the Nissan 90, and at 5000 rpm, I get approx. 39-40 mph. This is with a Michigan Wheel Vortex 13.25/17. I recently purchased a Vortex 13.75/15 that I want to try out for lower trolling speeds. The above speeds come from my sonar via paddle wheel, which I had calibrated with my GPS. It is difficult for me to rely solely on GPS, since we always have some sort of current in the bay. As is, the above number indicate almost 0 slippage which I doubt to be the case. In any event, I made some calculations, and with a 17" prop, if you have the 70C with a gear ratio of 2.15:1 (12:28), then at 6000 your "prop" speed would be about 44.9 mph, and with the 70B with a gear ratio of 1.92:1 (12:23), at 6000 rpm, your "prop" speed would be 50.4 mph. By prop speed, I mean disregarding any cavitation, flex, or hull slippage.

As for my specs, I am currently running with my speedometer on the sonar adjusted to -7%. That adjustment was needed to match the sonar with the GPS. The calibration was also done at a relatively small lake with no current and flat conditions. I actually suspect that my prop may actually be closer to 18" rather than the 17" as stamped on it. This is because I can not account for the fact that otherwise, I have basically no slippage. Any other assumptions would include either a faulty tach, GPS, or non standard gear ratio.

Sal, by the way, as I understood it, the prop shaft on the Mercs., Nissan/Toh., and Yamaha, (Maybe Honda) are identicle as far as diameter and # of splines (15). The only real difference was in the size of thrust washer. This may make fitting a stilleto a bit easier.

SpeedBump posted 04-16-2004 08:40 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Sal- Thanks for the info.. The day of my GPS run I was in the Bay at High tide and it was a high spring tide. Winds were light without much chop on the water. I would say there was little current factor in play.

I was quite suprised to find my FF paddlewheel speedo so close to the GPS readings. At WOT they really were off only by 1.5-2MPH. and at all ranges not more that 2 MPH. The 34.5 MPH was by GPS. I have not calibrated the FF w/the GPS.

I was carrying 22 gal of gas under consol, and myself 265lbs. The Nauset turned Eastport does have a Suntop but it was down. I wasn't heavily loaded for the day.

I don't like to over rev the engine, on one occasion last year I had a heat sensor/alarm go off after a long high speed run through a calm channel. While the engine was pumping water well I assumed it was due to running lean while WOT at @ 5900 RPM. The delimiter did not kick in and the alarm was not on for long as I backed down quickly and the engine apparently corrected any negative situation. I have been careful to watch the RPMs and try not to run above 5500 and prefer to cruise between 5,000 and 5300 when calm enough.

It will be intersting to see what I get out of the 19 pitch prop. Wish I could justify the cost of the SS prop but it doesn't appear that it will make that much difference.

Gear reduction ratio is 12:28.

SpeedBump posted 04-23-2004 05:41 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Picked up my new prop today. Tohatsu 13" Dia X 19" Pitch, #48 77346T45 19P. Hoping to get it installed and see the results this weekend. It is very different in shape than the elephant ear 17 pitch prop I currrently use. This one is a three blade cupped prop. The dealer I used indicated it is a mercury design. Has the mercury injection molded platic hub insert, a very nice brass thrust washer and bronze spline insert. If I spin the prop its off to a merc dealer for a replacement plastic bushing.

Now the reason for this post.. the dealer recommended a modification I would like feed back on from those that know props.... Sal D. and Sal T..

He stated if the hole shot suffered due to the increased pitch to 19" but the desired top end speed and RPM were achieved I could drill a quarter inch hole in the prop casing 1" in from the leading edge of the prop (Part closest to the Lower unit casing) and a half inch over from the weld on the convex side of the blade (back side of the blade where the blade is welded to the hub cylinder/casing).

He said this will allow for the thru hub exhaust gases to escape more readily causing the blade to come upto speed more quickly allowing the prop to grab at lower RPM and the boat will plane more quickly. He actually marked the prop as to where to drill these holes because if drilled on the wrong side of the prop he said the prop would be ruined and useless. Apparently he learned this trick a good number of years ago when he competetivly raced boats. Any comments on this method of tuning a prop would be greatly appreciated...

SpeedBump posted 04-23-2004 05:48 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Sal T - you are correct in your knowledge of spline design. Toh/nissan shaft is 1" diameter and there are 15 splines 1/16" in diameter (measured with a steel mechanic rule not a micrometer).
Salmon Tub posted 04-23-2004 09:29 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Is the plastic insert squarish and tappered? If so, then you have a Michigan Wheel Vortex prop. That is the same type that came with my motor (it was white and had 13.25x17 stamped on the hub). The original Tohatsu props are one piece as I understand it, but I have not seen any for our size motors. All the dealers carry the MW props and swear they are OEM. They used to be listed in metric sizes and If I am not mistaken, even the N/T web site now lists them in inches but funky sizes like 20.3" pitch. They may have switched to a US company to supply the OEM props. The Vortex is a decent prop, I have a 17 and 15 pitch, and use the same hub. I would not recommend drilling holes. If the prop is too slow on acceleration, then the dealer sold you the wrong product. Good luck.
SpeedBump posted 04-23-2004 10:41 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Sal- The insert is squarish and tapered. Prop is one piece cast aluminum part # 3EO-64194-0 . Intersting thing this prop came from Tohatsu America corp in Carrollton Texas.
Salmon Tub posted 04-29-2004 10:47 AM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
So, how did the prop work out?
SpeedBump posted 04-30-2004 05:40 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Sal haven't had an opportunity to get it on and tested. Hope to do so this weekend or next at the latest. will update once I run it a bit. thanks for asking!!
SpeedBump posted 05-07-2004 09:52 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Here is the update on the new Prop.

Got the new 13X19 Tohatsu prop (Michgan Wheel Vortex/Mercury prop) installed this afternoon. Splashed the boat and had a leisurely no wake cruise down the river to the bay. Didn't notice any difference at this speed @ 6MPH. Got past the NWZ and opened the boat up, hole shot was acceptable, jumped on plane by 3,000 RPM and zipped right up to 5,000 RPM WOT.

The engine didn't labor and the helm felt very solid. The prop didn't break water and there was a marked difference in the feeling of the boat's handling. It felt more sure of its self. Ran flat at a neutral trim, manuvered well in turns,it just felt more powerful, better handling.

Top speed was 35MPH at 5,000 rpm WOT with neutral trim. Tried trimming out a bit, tapping the trim control up a couple times brought the boat speed up to 37 MPH by GPS, on third bump and less than a 1/4 out, the prop broke water and the RPM went to 6,000. Held good speed in tight sweeping turns dropping from 35 down to 30.

My only concern is that WOT just got to 5,000 which seems a bit slow but is certainly better than the 5,800-6,000 RPM I was hitting with the 17 pitch WOT. It is amazing that I have @ 800-1000 RPM difference on these two props.
The other issue is of course hole shot. There were two of us on board + 22 gal of fuel under the consol. Hole shot was respectable similar to the old prop but perhaps a bit slower, I assume with three or four on board and hauling a tube this boat may struggle to get up on plane.

I am thinking to go with the vortex prop in a 17" pitch or having the cupping taken out of the 19 pitch that I just installed.

The dealer will exchange the new 19 pitch prop for a 17" pitch in the same cupped vortex design.

Any recomendations would be appreciated.

jimh posted 05-08-2004 11:03 PM ET (US)     Profile for jimh  Send Email to jimh     
It is always interesting to hear of how much a boat's ride and behavior can change with a change in propeller type. I think a boat's propeller is like a car's tires. When you change from bias-belted to performance radial tires, your car has a much different feel.

But you have confused me on the maker of this new propeller. Is it Tohatsu, Michigan Wheel, or Mercury? Or all three?

SpeedBump posted 05-09-2004 09:56 AM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Jimh- "But you have confused me on the maker of this new propeller. Is it Tohatsu, Michigan Wheel, or Mercury? Or all three?"

Good question - I believe the correct answer is .....all three.

The prop came from Tohatsu America Corp. in Texas as shipped to my local Nissan/Tohtsu Dealer.

I understand from the dealer that it is a Mercury designed prop that Tohatsu uses, which explains why it has a different shape/design from the original Tohatsu/Nissan prop that came with the motor.

Sal Tub indicates it is a manufactured by Michigan Wheel and is the Vortex model. From his description in an previos post I would agree.

Other than the part number stamped on the side of the prop there is no other mention of designer, manufacturer or distributor on the prop. the shipping box is another story all together, but nothing clearly identifying other than Tohatsu.

I agree with your comment about how much a change in the prop makes a boat feel. I was surprised at how much different it was. The tire analogy is a good one.

Salmon Tub posted 05-10-2004 01:06 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Jimh, as I have recently discovered, when it comes to 2-strokes, the prop plays an even more intimate role. I too have switched to a different prop, I went from the original 13.25x17 "OEM" Nissan prop, to a 13.75x15 Mich. Wheel Vortex. This switch was mainly due to the fact that I wanted a slower prop for trolling this season. The prop made quite a few notable differences. The first was WOT. WOT was 4900 with the "17", now is 5500 with the 15. A bit more than I had expected for only 2" of change. I previously would cruise at 3000-3100 rpm, at 24(+/-) mph (not nph). Now, I achive 18(+/-) mph at 3000 rpm, and at 3600 rpm, I run about 24(+/-) mph. So, when I used to run around at 3000, I now run at 3600 rpm. An increase of 20%. Here is where it gets interesting. My plugs have gone from almost black, to tan. I still have a bit more experimenting to do, such as read the plugs after a full day of trolling, but so far, the results have been good. I suspect that my previous prop, though stamped as 17" pitch, may have been a bit more, since at some speeds, I was getting negative slippage when calculated for a 17" prop. I have found a few interesting links to reading plugs and will post them in a new thread.
SpeedBump posted 05-28-2004 11:41 AM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
Finally exchanged the 13X19 Tohatsu cupped prop with a 13.25" X 17 Tohatsu cupped prop for my nauset. Boat runs well. RPM tops out at 5250 RPM. Top speed was 39MPH GPS and 39.5 FF, that was with 26 gal of fuel and one hefty adult.

Gets on plane at @ 2400 trimed flat. Hole shot about as good as the 19 pitch was. Biggest difference between the two is the 13 X 19 made the boat feel it had more power and the prop more bite in the water. The 13.25 X 17 feels similar to the original elephant ear prop.

Boat still handles better with current set up, less porposing and you can feel the subtle difference in the way the boat rides in the water. Biggest advantage is not over reving the engine, 5250 RPM is in the spec range WOT.

Plan on having the old prop reconditioned and keeping it as a spare.

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