Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

[wellcraft19]

Looking for a few inputs before switching prop...

Engine/outdrive combo: VP AQ171C (SP-A)
Boat: Wellcraft 192
Normally running 3-blade, RH 14x19

Been running 3-blade 14x19 (dia x pitch) for a few years. Works great, better than the 14x21 that does increase top speed a bit, but also barely allows the engine to reach WOT, and makes the hole shot trickier.

Was not aware that you could find 4-blade props for the older style VP-drives until I did track down Solas props. Since they are better priced than anything 3-blade I can find locally (about 1/2 price), figured out I'd give it a try.

Not looking for speed, but better "efficiency" and faster on plane. Good cruising speed is about 20-22 knots (can top out at about 42 on a good day). We also do a lot of cruising at about 5-7 knots in the city, maybe even the majority of nautical miles is at this speed.

Even with a properly adjusted trim fin, I do get a bit of torque steer - w/o adjusting the power trim. Slower speeds, trim is "perfect" for boat pitch, and when speeding up, if I don't trim down, torque steers appears. Once "trimmed", no issues.

Any idea if a 4-blade will help a bit with the trim issues?

I know Solas only make 14.5x17 or 14.5x19, and my gut feeling is to step down to 17 pitch (up .5" in diameter, down 2" in pitch, and add a blade). Or just stay with true and tested 1417 3-blade?

Most Volvos of this vintage were delivered with left hand rotating props. Mine has always been RH. Should I change when at it?

Appreciate any inputs!

Happy 4th!

 

[craze1cars]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

I had bad torque steer with my 3 blade factory aluminum on my Volvo (SX...newer than yours, mine on a 20 ft Stingray runabout with about 250 HP V8.) I switched to Solas 4 blade and the torque steer disappeared ENTIRELY....and planing speed improved as well.

I feel you are on the right track and will benefit greatly from changing to a 4 blade.

I did find I needed to drop pitch by 1" to maintain my RPMS with Solas 4 blade. 2" might be a bit much. Are you already at the very peak of your RPM range with the 19? If you have a little more room to move, go with a 17. But if you are already at your peak, a 17 might over-rev...

To further complicate things, I was right in the middle. 19 overrevved, 21 underrevved. So I paid a shop to repitch my 21 to a 20. Just right...

You may find the need to do something similar. Choosing pitch is not real easy when switching to extra blades and changing prop design....

Hope this helps!

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Thanks craze1cars,

That's the exact feedback I wanted!

Unfortunately Solas does not seem to make an 18 pitch, and with increase in diameter + the added blade, I hope to "do" with a 17 pitch. Rarely run it WOT (and boat has not been in the water yet this season so no chance to test at the moment either), but from what I can remember, I can hit WOT with the three-blade 19 pitch, but not with the 3-blade 21 pitch. Hence, I'm likely between a rock and a hard place. 19 pitch to steep, and 17 to flat...

One is a bit limited when it comes to props on the older Volvo drives, but once house is done, I will trade up to a slightly larger boat with a Volvo SX drive and a V6/V8 (easier to find parts than my current engine and a tad more power).
Will order one today and see where it'll take me.

 

[rkcarguy]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

I have a Aq131a in a newer Maxum, and ran into the same thing. I was turning 5350rpm with a 14x17 3-blade, which ended up having a slightly tweaked ear from a kelp encounter and pretty bad prop slip.
I went with a 14.5x17 4-blade solas and it's real close to being overpropped, but a new 14x17 3-blade got me back where I wanted to be. I'm working on a heavily modified cylinder head which I'm hoping will boost my performance beyond that of the AQ151 so I can easily spin that 4-blade past wot spec....

Now...being you have the extra umph of the dohc AQ171, the 4-blade 17 pitch solas amita should set you up nicely. You will likely pick up some cruise speed, get better slow speed maneuvering, better holeshot, but will loose some top speed.
That's impressive, the top speed of 42 mph by the way...

Post results once you get the prop and try it out. Not too many of those motors out there anymore, and that would be valueable info.

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

hi rkcarguy,

You are correct, not too many of these (the last and final) "real" Volvo engines out there. Too bad in a way, a pretty powerful engine for its size, reasonably modern with a DOHC, cheap on gas, but due to its "rarity" scarce (or impossible) to find when it comes to parts.
On the other hand, these engines are highly sought after from those who use the old Volvo cars for rally cross...

Can I ask you one question, seeing that you have a 2000 maxum 1900SC, converted to Volvo AQ131/275. What happend, or what triggered this change?

 

[rkcarguy]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

I had a good running, but rotting 86 Capri, and a 2000 Maxum 1900SC bank repo with a freeze damaged...more like ruined... 5.0L merc and no drive came along at a price too good to pass up.
The volvo transom "hole" is alot bigger than the merc, so I did the pattern layout, drilled and cut the volvo pattern into the transom and swapped everything over.
The cool part is, if you look at boat-test, this boat got a best of 3.3mpg with the test driver and 1/2 tank of gas when equipped with the 4.3L Merc.
With 3 people, full tank, kicker motor, coolers, and fishing gear I see 4.2-4.8mpg depending on conditions.

Your AQ171 is a cool motor indeed, but when you need a new exhuast manifold that's not going to be a wallet freindly experience. Most other motor parts can be found or crossover except for that and the marine cams.
I'd end up having a manifold fabricated if I was to ever convert to DOHC, no spark plugs in the way like the SOHC would make it easy to do..basically box in a nice heavy wall tube header.

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Ah, never thought about that. Might be one way to go. Boats are cheap when the fall comes here in the PNW.

BTW, you can buy a stainless steel manifold from a shop "down under". About $3,000 AU...
Although very sweet looking, but almost looks like it's cast and not welded. eBay item #130017198071

Do you by any chance have a good source (or cross ref) for the timing belt, the water pump, and the idle pulley? Heard a lot during the years, but really no substantial sources.

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Update: The Solas Amita 4-blade (14.5x17) arrived today.

A few reflections:
Packing from iBoats.com - outstanding!
Solas package: innovative and very protective (compared to MW and Volvo I used in the past).
Prop "looks" great, certainly more cupping on the tailing end of the blades than any I used in the past.
For the monies, this looks good so far.

See if I can get it out next week and try it out. If you read above, I'm going from a MW 3-blade, 14x19 to a Solas 4-blade, 14.5x17. Earlier tried with a Volvo 14x21 but that was borderline too steep of a pitch (and that prop is happily resting at the bottom of the lake due to me poorly tighten the cone/screw - http://www.kirklandviews.com/archives/21310/).

 

[rkcarguy]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Turbobricks has alot of info regarding the DOHC AQ motor, where to get parts, belts, etc.
I almost did the conversion to my SOHC, but it would have been a handfull getting carbs and a marine manifold...basically big $$$ for the marine parts or custom fabbing both manifolds(I do fab at home)...
There's a guy in Lakewood, WA that welds up some nice turbo headers for various volvo engines. I was looking at having him make a header ~$650, then box it in with 12ga stainless.

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Ah, thanks for the info. I know about Turbobricks (and have a few Swedish based sites as well), but interested in contact info to the guy in Lakewood. Will likely have to have a manifold made one of these days.

 

[rkcarguy]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Nathaninwa is the guy on TB that does the fab work on intakes and headers. He's got a DOHC converted motor making around 400HP with a big turbo on it.
When the time comes, take your old one in so he can match up the fittings, have him build a header and then box it in with stainless sheet metal.
The hardest part, is you either need to run bolt tubes all the way thru, or sleeve each exhaust runner while still leaving enough room to get a bolt/nut on to the head studs.

 

[clemsonteg]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

You had asked me in my thread to post my results from going to a 4 blade prop. Went from a 3 blade 13.75x15 to a 4 blade 13.25x13. My rpms and speed actually stayed about the same so all I did is reduce my slip. I'm considering having the prop repitched to an 11 to get it in the right rpm range.

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Clem,
Thanks for the info. I will post my results as soon as the boat's hit the water (going 3-blade 14x19 to 4-blade 14.5x17).

Yeah, I know, the summer we never had is nearing its end, but have been/is busy working on the house, so boat's got to wait a little bit longer. New 4-blade prop still sits in its nice box under my desk here in the office.

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Boat FINALLY hit the water (first time this season) yesterday with the new (Solas 14.5x17, 4-blade) propeller.

The Lake and the Sound were a bit too rough to do some serious testing (wife and dog on board does not help either for that), but a few impressions:

1. Took a while to get the trim fin adjusted, and I have some more fine tuning before all torque steer goes away.
2. Going from a 14x19 (3-blade) to a 14.5x17 (4-blade) might have resulted in a tad too low of a pitch, just a feel since I could never run it WOT yesterday due to remaining torque steer (while trimming out) and lake conditions.
3. Boat seem to plane at lower speeds, already at GPS speeds of 12-13 knots (I think before I had to reach 15-16 knots before planing comfortably).
4. Lower planing speeds come at the "expense" of higher engine RPM. 1,800 RPM resulted in 5.8 knot, 2,000 RPM in 6.5 knot, and 3,500 RPM in about 15 knots. Instinctively, this is higher than I ran last summer with old prop.
5. While doing a bit over 15 knots, and "trimming out", significant rise in exhaust "growl". Doubt it is due to "ventilation" (older VPs do not have through-the hub exhausts) and since I do not drop anything in speed, but maybe rather due to the fact that a 4-blade might "lift" the stern a little bit more than a 3-blade (but very eager to hear other people ideas here - as I am no fun of a noisy "throaty" exhaust, and really cherish this boat's normally quiet running).

The (old) 3-blade 14x19 is currently at the shop getting a tip of a blade repaired. So in all seriousness, will not 100% be able to tell the differences until I can run these two props "back-2-back". Hopefully that can be in a week or two, but my gut feeling is that a 14.5x19 (Solas does not make an 18" pitch) would likely have been a better choice, than going all the way down to the 17" pitch.

Maybe not surprisingly, but the Solas looks "brand new" even after one full day out. Most props I've ran have shed a little bit of paint on the leading edge.

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Yet another update with my 4-blade adventure.

My old 3-blade 14x19 is either a Volvo OEM or a Michigan Wheel (prop still at the shop, so not 100% on the brand), but that prop carries the boat nicely.

As you can see from posts above, I went down to a 17" pitch when I picked up the Solas 4-blade. Going to 17" pitch makes the boat horribly under propped. Had some time to try this morning, and could easily rev up to 6,000 (yes, the AQ171C is a high-revving engine, although that is a tad high), and still not reach more than roughly 26 knots, a drop of more than 16 knots (considering that 42 before would be around 5,400 rpm).

The Solas works well, but I really think I should have stayed 19" pitch. No idea of the Solas is not as "aggressive" as the (standard) MW or Volvo aluminum prop, but in my case, following the recommendation to dropping 1-2" in pitch while going from a 3- to a 4-blade was not the right thing to do.

Part from me picking a tad too low pitch, the prop looks like new, seems to allow the boat to plane earlier (today just above 12 knots, but only dog and me on-board), and I had really good "bite" when I did some crazy sharp-left to sharp-right maneuvers at decent speed.

Once I got the old prop back, and I can truly test them "back-to-back", will report more (assuming our amazing weather will hang around).

 

[wellcraft19]

Re: Propeller sizing, going from 3-blade to 4-blade on a VP SP-A drive (AQ171C)

Last update for the season, since Saturday most likely was the last run.

Empty boat, part from first mate (100 lb dog) and me. Full fuel tank; Hitting 29.5 knots (GPS) at 5,000 rpm (still much lower speed than before).

Point 5 in #13 above. The noise (growl) is still there. I start to wonder if it really is exhaust noise, and not actually ventilation noise (even though I don't really loose any bite. Just so weird the drive would let of this "growl" as it has never done it before this new 4-blade prop.

And no, my old 3-blade 14x19 has still not been picked up. The shop is "out of my way" and close at 5 PM. Hard to actually get there to pick it up.

The experiment continues, albeit I start to think that my 3-blade might been better over all...

All the while, the Solas truly still looks like brand new. Not a mark, no paint gone, no tips "sanded". Seem to be of good quality from that perspective.