Propeller

[Jerry]

I think I remember a long discussion on the past Forum regarding propeller selection for the 20HP Honda. I can not find it on this one. Unfortunately my memory is not as good as it was but after one season it is one of the items I think I would like to change as well as adding an RPM/Hour gauge to Peregrine.

Can anyone let me know what they have found to work the best for a prop?

[Ron]

For the 20 hp Honda, I've been using a Solas 4 blade 10 inch diameter x 7 pitch aluminum prop. Price is reasonable too - chech iboats.com for a pretty good price (around $60 as I recall). You can buy the exact same prop from Honda for probably double the price. It's what they call a "Power Thrust" propeller. It's got 4 bigger blades which push more water. RPM tops out at around 5600, max speed is just over 8 1/2. 3500 rpm will get me around 6 knots depending on sea state. Honda used to make a 10x7 5/8 but it's no longer listed in their catalog. It was also a LOT more expensive than the Solas (and it was made by Solas for Honda) and I couldn't find it at any price. Numerically, the 7 5/8 pitch is probably perfect for the boat. The other Honda or Solas props are not Power Thrust.

The standard prop was something like 9 1/4 x 10 or so. Those who tried to measure the highest rpm all reported around 4,000, which is way too low. Dan is using a composite 3 blade which he liked also. That prop was something like 10x7 as well.

I don't think any of the 50 hp owners ever played with their props. I imagine that the standard pitch is also wrong. There's a world of difference between a 1500 pound runabout that can do 30 knots to a 4500 pound trimaran that won't break 15 (with the 50).

[Dan]

Ron's right. The prop I am using is 9.5 x 7.5 three-blade pirahna composite prop. It's an excellent choice, though a bit more expensive than the SOLAS one that Ron is using. However, IMHO the composite prop has a few advantages, not the least of which is being able to replace individual blades and carry individual blades. The Pirahna's blades are designed to shear in the case of a hard impact, which may prevent damage to the lower unit.

[Ron]

Forgot about the tachometer part of your post. For several reasons I wanted to use one of the Honda supplied tachometer/hour meters. These just plug into the Honda harness - no electrical work to do. There were a few to choose from (Honda, Faria, Teleflex, etc.) - the Faria / Honda unit with the black face seemed to look the best, and was the lowest price. Honda part number is 37250-ZW5-010ZA. But I did not really want to pay an inflated price for it from a Honda Marine dealer, so I googled the part number and found a place called M&D Mower in Ohio who was quite willing to sell it to me for about $70. The marine dealer want about twice that. Second thing was that putting it on the port side under my feet would not make it easy to see - so I picked the same location on the starboard side. The cable is about 8 feet long so no problems there. Use a hole saw (forgot the size) and clamp it in, run the wire across the transom, and plug it in. There's a plug near the engine remote control that looks like the opposite of what's on the tachometer.

The various Honda gauges are below -

http://www.honda-marine.com/catalog/pdf ... Gauges.pdf

These are the props -

http://www.honda-marine.com/catalog/pdf ... ellers.pdf

Pick up one of the small in-line Racor gas filters / water seperator's as well (and a spare cartridge or two). Better to change a filter cartridge than have to rebuild the carburetor. Part number is 025RAC02. All-Points Marine had the best price 2 years ago, but google it first to see what's happening now.

One other note - the oil drain plug and lower unit fill and drain plugs are large head metric screws that tend to get distorted slots from using screw drivers when torqued to specification. I'd pick up a spare or two to keep on the boat, and a few O-rings. Use the biggest driver that can fit in the slot - maybe a socket based one if you can find it.

[Jerry]

Ron/Dan,
Thank you both - I already changed both the engine and lower unit oil so I know what you mean about the slots. I was glad the boat was home so I had my entire screwdriver set to work from. Spares are a good idea.

[Ron]

I was able to track down the new part number for the 20hp 4 blade 10x7 5/8 Honda Power Thrust prop. It's 58130-ZY0-B92ZA. Best price is at boats.net - $79.99 plus $8.95 shipping. Last year a dealer wanted about $160 (old part number). I ordered it and should have it in about 4 or 5 days. The 7 pitch worked pretty good, but I was doing around 5600 rpm at wide open throttle. In spec, but a little high for my tastes. This should cut down the wot rpm to around 5200, exactly where I want to be. Crusing speed should go up by around 9% as well, maybe top end too. I'm shooting for over 6 knots at 3,000 rpm and 9+ at 5200. The motor develops its maximum torque at 5,000 rpm.

I'll report back after I install it.

[Ron]

OK, the Honda 10x7 5/8 4 blade prop arrived yesterday, installed it on the boat this morning, and went for a sail. I was a little surprised at the shape of the prop - the blades are slighty smaller than the Honda/Solas 10x7 version - but they seem to have more of a compound curve in each blade. I figured this would be a wash - the slightly greater pitch would be neutralized by the slightly smaller blades. Didn't work out that way. Not quite the gains that I expected, but still better overall than the 10x7 Solas.

Wide open throttle on the Honda 10x7 5/8 was about 5,000 rpm. The Solas was doing 5,600. Both are within specs. The 20 hp Honda delivers maximum torque at 5,000 so there is really no need to go over that. Honda wins then.

Very little, if any, gain in top speed. Got up to almost 9 knots at 5,000 on the new prop vs about 8 3/4 on the Solas, but it was doing about 5500. Honda wins again- slightly higher speed at a lower rpm within allowed specs.

Cruising speed was definitely improved though - I was doing about 7.3 at 4,000 rpm, and around 6.25 at 3,000 on the Honda prop. That's probably 10 to 15 percent better than the Solas 10x7.

Anyone buying a new prop for the 20 should go with the Honda Power Thrust 10 x 7 5/8. If you aleady have the Solas 10 x 7 I probably wouldn't bother to upgrade. I got the Honda prop at boats.net. Part number (Honda's) is 58130-ZY0-B92ZA. Total price with shipping is about $88.00. The prop would cost around $120 at a dealer.