CONTINUOUSWAVE

I have a 1965 Classic 16 with a 2000 NISSAN 50-HP Model NS50D2 two-stroke-power-cycle engine using a stock propeller. The engine weighs about 180-lbs. I just had it out on the water the other day and [the boat] ran perfectly - but I think there is some room for improvement in speed and economy. This is a great little set up and I'd like to get the most out of it.

[The boat speed] topped out at about 30-31 MPH, engine speed was 5200-5300 RPM trimmed out. Maximum RPM per the manual is 5150 to 5850 RPM. I'd like to get to about 5500.

The engine seems to be mounted a little low. I'm thinking I could raise it about an inch or two up using current mounting holes. On top of that, I want to upgrade to a stainless steel propeller or a better propeller that would provide more performance.

Gear Reduction per the manual is 13 : 24

Does anyone have a suggestion on the best propeller to use for this set up?

Would a jack plate (manual) improve performance any?

M -

Keep in remember, you have a motor that is 1/2 the rated maximum.

If you want to improve performance, I would raise the engine 2 bolt holes and retest. Typically, raising the engine 1 hole raises the WOT rpm by 150-200 since there is less lower unit in the water. You have room to go before hitting WOT.

This is a DIY and can be done on a trailer.

A jackplate will not generally help increase speed and adds weight.

I understand I have half the rated horsepower on the boat, but I think the benefits of having a light engine on this non-smirked hull are severely overlooked. This boat handles great and feels well balanced. I can cruise at 25-MPH all day, which honestly, unless the sea is flat calm, is plenty fast. At this point I'm looking to maximize handling and efficiency while reducing draft.

I can only raise the motor one hole up using existing mounting bolts; see the picture. I will do that this weekend. Do you need a engine lift? Or do you use the trailer jack to raise and lower the engine mounting height?

[Give] suggestions on a propeller.

Thanks.

I would raise the engine using trailer jack.

Would want to read the results and see what WOT rpm's you can get before changing props.

Peter has a good recommendation here: http://continuouswave.com/ubb/Forum4/HTML/005862.html

I will raise the engine this weekend and hopefully get out one of these days to test.

[Give me an] idea of the fuel economy of this set up. I've never gotten around to testing, but I figure I must get be getting [over] 6-MPG cruising at 4200-RPM and boat speed of 21 to 22 MPH.

Usually a classic two-stroke-power-cycle outboard engine will have a brake specific fuel consumption of about 0.55-lbs/HP/hour.

For a 50-HP engine running one hour, that is 50 x 0.55 = 27.5-lbs/hour fuel consumption. For gasoline that has a density of 6.25-lbs/gallon, that will be a fuel flow rate of 4.4-GPH.

If your boat were getting 6-MPG, then the boat speed necessary to get that economy from a burn rate of 4.4-GPH would be about 26.4-MPH.

I was able to raise the motor this weekend. Take a look at the pictures and let me know if this seems right. It was raised just about 1.5 inches. I was not able to use the top mounting holes, so I will either have to fill them up and drill new ones, or test using the outboard clamps. The bottom of the bracket is through bolted.

Make sure you have those holes sealed of preventing water from entering your transom.
After testing replace that aluminum prop with a stainless one using any prop selector found on the internet. Higher RPM = lower pitch.

Update - I was finally able to test the boat with the new raised engine height. I was able to hit 5500 RPM trimmed out. Before motor was raised I would bounce around 5200 RPM. Boat speed surprisingly did not change much, I still topped out at 31 MPH. I put 40 miles on the boat through some pretty rough weather at times and she handled fantastic.

Now I'm thinking about changing the OEM prop to a good stainless steel prop. Any recommendations?

Thanks

With a WOT of 5850, gear ratio of 1.85:1, 5% slip and a target speed of 35, the prop calculator suggests a 13" pitch prop.

A respected member on this site, Peter, recommends the Stilleto's Triad II in 10.5 x 13 for your engine.
http://continuouswave.com/ubb/Forum4/HTML/005862.html

A whaler prop guru also recommends the same prop. See 4th before last post in this thread:
http://continuouswave.com/ubb/Forum4/HTML/006024.html

Dan's Discount Prop's is a respected vendor by many in the whaler community. See item #8023130013 here:
https://dansdiscountprops.com/BuyNow/stiletto.cfm#triad2

Thanks for the help - unfortunately Stiletto has been out of business since 2013 or so, and the website you linked does not have any stock

I know a 15 Sport owner who runs a 2005 Nissan 50. He is running a 11-1/8 x 13 Solas New Saturn. Part number 5331-111-13. He is very happy with its performance.