Honda 3 or 4 blade aluminum props
So I put on a new set of aluminum 3 blade 17" pitch props on the Koffler (28' w/twin 150 Hondas). The boat had stainless 15" pitch props when I got it but it ran about 6200 rpm's.
Took a group of hunters to Esther passage on Monday and the boat was heavily loaded, took a while to get on step so now gonna try a set of 15" pitch alum props. I'm anxious to try a set of 4 blade props from A1 but they won't have 'em in stock for a few days and need to run the boat this Friday so the 3 blade props from A1 it is.
Anyone have experience with the 4 blade version? Also considered installing a set of dol-fins on the motors but will progressively make changes after prop swap. The boat has trim tabs. Also my buddy says the the 4 blade props should provide some stern lift which would be great.
On that note if anyone has a set of 3 or 4 blade 15" pitch aluminum honda props they wanna sell or even loan, please holler!
Ps- need to run aluminum props beaching the boat quite often
I have put a set of Doel Fins one every boat I own because they work at getting a boat up on plane faster than with out. They excell at allowing the boat to be on plane at a slower speed, which is important when running in snotty weather. I have run a few different props on my landingcraft with a Honda 90. The boat had a four blade prop on it when I got it. I tried a 3 and 4 blade prop, and also a few different pitchs on the 3 blade. It came down to I got the best all around performance (loaded and unloaded) with the lowest pitch three blade.
Being a heavy guage welded 22' with only 90 hp, it was important to have the right prop. I run it fully loaded and empty and I get great performance. It is propped to reach the max 6000 rpm when empty, yet it still pops up on plane when heavily loaded. The motor is still peppy at all speeds loaded or not.
With twins I suspect you will be just fine with three blades. You have enough HP for that boat. My friend here in Juneau had a 28 Koffler with twin 200HP HPDIs, it had an unfortunate ending one winter and sank (scuppers were too low and got pushed under due to snow while at the dock). Hmm come to think of it, it got purchased from the insurance company and got outfitted with twin Honda 150s. Motor life will be increased when the engines are not being over worked. If the motors are sluggish to respond to throttle changes you have too much prop.
You can achieve sternlift with 3 blade props too. I remember a friend of mine who had a 19' Boston Whaler (trailer queen which wasn't water logged as some whalers are) and it had a stainless offshore prop on a 150 Merc. That boat refused to plane out, so I bought him a stingray fin, and it still was slow to come out on plane. When it did thought that was a 60 mph boat. Only the prop was in the water it seemed. After a while we read that the prop it had on it (from the dealer) was a bow lifting prop for offshore use. We wapped out to a standard prop with more stern lift and viola we had a much better boat.
Also placement of people and gear makes a big difference as well.
Here are the specs on your motors from Honda.
Dropping from a 17 to a 15 pitch will lower your rpms about 400rpms, should get you about right.
Type 4-Stroke DOHC 4 Cylinder/16 Valves
Displacement 2,354 cc (144 cubic inches)
Bore & Stroke 87 mm x 99 mm (3.4 x 3.9 inches)
Full Throttle RPM Range 5,000-6,000 RPM
Rated Power 150 HP @ 5,500 RPM
Cooling System Water Cooled
Fuel Delivery Programmed Fuel Injection
Ignition System MicroComputer Programmed
Starting System Electric
Exhaust Through Hub
Lubrication Wet Sump
Trim Range -4° to +16°
Tilt Range 72°
Gear Ratio 2.14:1
Gear Shift F-N-R
Alternator (Electric Start) 51 Amp
Battery Charging Power 30 Amp (1000 RPM), 40 Amp (2000+ RPM)
Power Tilt NA
Power Trim & Tilt Standard
Gas Assisted Tilt NA
Oil Pressure Alert Standard
Temperature Alert Standard
Speedometer Pickup Standard
Overall Width 580 mm/22.8 inches
L-Type 217 kg/478 lbs.
X-Type 220 kg/485 lbs.
L Type 508 mm/20 inches
X Type 635 mm/25 inches
Well loaded the boat with 4 hunters and enough crap to last a month instead of just the 4 days they'll be out. Before we even left the dock I swapped the 17" for the 15". Barely got on step and 19 kts, eventually got 23-24 kts at 5,000 rpm's. Relocated stuff to the bow but didn't help much.
For the pickup will run the stainless 15" mad see how they do. On the return trip after dropping them off, ran the 17" alum props and could only get about 5200 rpm's. But cruised the 60 or so miles back at 25 kts at 4500 or so rpm's. Could only top out with the 17" props at 5200 and 33-34 kts. Probably a bit too much prop?
Yep...that 17p is WAY too much prop if unloaded cannot even get above 5200. AL props perform differently that the stainless for sure. With care, shouldn't be a problem beaching with the stainless prop, if you are careless with the AL, sure the prop will break more easily and possible save the lower unit, but then where does that leave you?
When you are alternating loaded extra heavy with running empty, there is no way to get around prop tradeoffs. The only reason NOT to have a prop that exceeds the 6000rpm threshold is if you run wide open...that 15p stainless is going to save a lot of stress over the 17p/15p AL props. I would run it and just be careful when running empty...and I would bet it will be under 6000rpm when loaded.
I went to a 4-blade AL prop on my old boat, and what I found was huge improvement getting on step, but I gave up a lot of top end and used more fuel running at cruise, about 24knots. IMO, the performance of stainless props makes them the best bet, you just have to be even more careful not to hit rocks, because they are so strong and will be more likely to cause lower unit damage if you do hit something. Your pitch should be set at your normal loading, and for you, that means a very heavy load. You want to get to at least 5800rpm at WOT with whatever you are using when loaded, or you will be lugging your engines and putting excess wear and strain on them
Thank you for your experience & insight Capt Ron, on both threads! Will hopefully have better news to report tomorrow!