Aquasport Mechanicals - things that need a wrench, screwdriver or multimeter > Props

1985 196 Model with Suzuki DF140A

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cryder:
Hi All,  I think I've got this dialed in now so just an FYI to the group. I had a 2001 Honda 130 on this boat (1985 196) with a 4 blade 13.25x15 prop that maxed out at about about 5400 RPM.  Over propped I know and I used this about 4 times before the rot in the exhaust port killed that engine. I am guessing it went 35 or so with this but was a VERY comfy and easy plane at about 4400 RPM.  I just bought a 2021 Suzuki DF140A and with a 4 blade 13*19 it turns 5400+ (still over propped I know and I have a lower pitch on order) but it's much slower as the Suzuki has a 2.59:1 gear box (when they went to the 'A' as in DF140A they went to a 2.59:1 gear box where as the Honda (and old Mercs and a Yamaha F150) have a 2:1 gear box.  The BIG (and I mean HUGE difference here is that the Honda or Merc or Yamaha at 4000 RPM's turn the prop at 2000 RPM.  The Suzuki needs to turn 5180 RPMS at the power head to get 2000 rpms at the prop.  So planing speed with a Yamaha may be  4000 RPM but with the Suzuki it will be nearly 5200.  I have an excel spread sheet that goes over this math.  The Suzuki is lighter BUT if you have a light boat like an Aquasport you don't need to worry about working the engine too hard to get up onto a plane.  In theory the Suzuki turns a bigger prop but slower and I must be honest, IMHO, the old Honda had a better hole shot and planed the boat at a lower RPM.  I attached my prop calculator for folks to mess around with.  The big variable in this is the prop efficiency.

RickK:
I'm having a hard time reading the temperature of this post. Are you disappointed with the Suzi?

Tampa Bay Mike:
Seems like there may be something else going on. I've got a 22-2 with a 140a running a 20p four blade and I'm closer to 6000 rpms. Seems like you should do better than 5400 with a 19p.

cryder:
First, RickK am I disappointed with the Suzuki?  Yes, and No. Sorry. The thing runs and it's super duper quite which I love, love, LOVE.  And with the warranty I wont have to think about it no running for a long long time. BUT the 20 year old Honda, even though its' 100 lbs heavier, produced FAR better performance results IMHO. I failed to take into account the difference in the RPM's at the prop between the options.  If I had I may have bought a 115 Yami. I was happy with the Honda performance at 4400 RPM but the zuke needs 48-5k to get to the same planing without the ass dragging speed and it never gets to the OMG hold on speed which the Honda did.

Tampa bay Mike, yes I thought I would see better speed and in fact I asked the dealer to prop it for power, not speed, as my 17 year old daughter will end up using this boat and with the 130 HP Honda that was under pushing the 15"P prop it got "squirelly" at top speed. In looking at the performance sheets I failed to note that the 140A has a 2.59:1 gear box where the older 140- has a 2.38:1 gear box.  The boat has been sea trialed 3 or 4 times by the dealer who first tried (1st guess) a 3 blade 19", then a 3 blade 17". I was on the boat for that one and told them I expected both more power and speed and asked for the 4 blade to pick up the stern. After the sea trial I told them to forget the BS of first instructions and get the thing to move. I was then told that a mechanic had detuned the engine buy not allowing the butterfly valves to open up based upon my note that the engine be propped for power not speed.  I was happy when I picked it and saw the 4 blade 19" until I got to running around a bit.  A 20' boat with a 140 should fly and it's still slugish and that was with about 30G (/50G) of gas and just me, no kids, coolers, no gear.  Bottom line is that it's fast enough for me but I liked the idea of being able to run the engine down around that 4500 RPM range.  I'm still playing with it though.  I hope to have better results to report later.

cryder:
Hi All,  I'm going to revise ALL my rants about the Suzuki. The story is. I ordered a new engine. Without asking me the dealer installed a counter rotating unit on my boat. It should not matter but on my boat the starboard foam has water in it so the twist of the counter rotate accentuated that lean. The dealer said the Suzuki props were back ordered and put on a 3 blade 19".  Anyway the numbers above were with that now old engine and I swear it was just 'a bad engine'. At sea trial I was disappointed with the lack of gusto the engine had so the dealer put on that 4 blade to try and improve that.  The replacement engine (same DF 140A but a standard right hand rotation) runs great with a 3 blade 14" dia. x 19" pitch used SS Powertech LNR3R19PSF115 prop.  The engine tops out at about 6000 RPM (I did not push it as I'm still in the break in period) and I plane comfortably at about 45-4600 RPM (30 MPH).  The counter rotater had a 4 blade 13x19 but based on what I've heard from others I will probably not go to a 4 blade but perhaps a 3x14x20?  Once I'm out of the break in I'll do some testing with a GPS and post some speed numbers.

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