MV 34 - 4 blade props

[DickTuschick]

Hi Folks! Yesterday I had the most facinating experience on a PDQ 34 in a LONG time. I took Harvey Griggs' new boat (has the 100 hp) out for a sea trial on the St Lucie River. Harveys boat has the new 4 blade props and what a difference !!!! It is the most remarkable improvement in the PDQ I have seen is a long time!! There was vertually NO vibration noticeable and when I went down into the salon I could not believe how quiet it was, almost like driving a car....it was THAT quiet!! I did not take decibel readings, but a guess would be at least a 50% reduction in noise at 3000 rpm. I also noticed a significant decrease in cavitation when in rough water.
I'm sure there will be a lot of discussion about why the difference is so significant but in my experience the subject of props is a bit of a "black art" and not all that scientific.
On the performance side, the speeds/RPMs were identical with the 3 blade props I have on our boat HERON. Top end was about 3700 rpm at a speed of about 19 knts.
The company that supplied the 4 blade props (H&H Propeller) is the same company that supplied PDQ with all the running gear so they are very familiar with the boats.
I have been led to believe that there is an appropriate size that will replace the smaller props used on the 75hp engines that will give the same benifits.

Backing up a bit, PDQ did start delivering the 34 with 4 blade props (the last 4 0r 5 boats they delivered) along with the new 110 hp engines. At the time, we knew that there was a significat improvement in noise level and vibration, but there was no way to tell, for sure, if it was the props or the engine or both. NOW WE KNOW!!! It was the Props!!

Given that we have now experienced this improvement with the new boats that were delivered with the 4 blade props AND a retrofitted 100 hp boat I suspect that a comparable improvement will be realized on all boats.

Based on the quantum improvement these props make, I have a feeling that a lot of owners will want to upgrade. I have contacted H&H to see if we can negotiate a "quantity" discount if we place one big order and drop ship to each owner individually. As soon as I have more details on the pricing I will update this subject on the forum.
Safe cruising,
Dick

[Mishigas]

Thanks Dick, keep me posted regarding the prop upgrade. If they offer one for the 75 hp engines, I would be interested. With the reduction in sound and vibe it certainly would be worth considering. Regards, Sandy Kramer MV MISHIGAS Hull 68

[Tom Green]

Dick

Thank you for this information. We would be interesting to changing to the 4 blade props.

We had aqua drives installed after we purchased our boat here in Seattle. I can tell you that made a major difference in noise and vibration also.

Thanks again and Happy Thanksgiving.

[Kama Kat]

Happy to hear about your good experience with the four bladed props. Kama Kat has been using such props since 2004 ....we are fitted with 75HP engines. Once, while our props were being repaired, we ran with three bladed props for about one month .......never want to do that again.

[duetto]

hi frank,

what pitch & diameter do you run? how loaded is the boat usually? can you make 3800-ish rpms?

[Kama Kat]

Hi John,
Our original props were four blades, 16in. diameter with 13in. pitch.
When we did sea trials with PDQ in April 2004, at time of assuming ownership, with three people on board, no dinghy and otherwise "empty" ....(their low fuel and water level, for functional testing purposes), Kama Kat registered 17.2kts at 1750RPM. September 2004, fully loaded for cruising, with all tanks FULL, including dinghy but no bimini, our tests on Lake Ontario showed about 16.2kts at 3650RPM. These were the "good old days" of performance, before we added a bimini and various spares for the"America's Great Loop" in 2005.
As cruisers, we travel 5-8hrs per day. Yanmar reps. suggested that running that long continously at 3200RPM is not a great idea if we wanted long life out of the engines. It was recommended that 3100RPM was a better max. for daily, prolonged cruising. I fully agree with this! So, being able to run up the engines to 98% of rated maximum RPM only shows that the boat is NOT "over-proped" for the engine capacity, loading and sea conditions . Actually, if one did manage to reach 3800RPM with the engines, fully loaded, etc., I would conclude that the prop. diameter/pitch were marginally on the small side.
In 2006, we changed to 17"X13" "skewed" props with a view of improving fuel consumption and yet reducing prop. noise/vibration. This change went with the addition of a fully enclosed bimini, change of main anchor and increased chain length to 100ft., and carrying old anchor and chain as #2, along with original props as spare, full set of zinc spares and tool kit to be able to do repairs ....including prop. replacement. When we go south for the winter, we also carry two bicycles and my kayak. In addition, of course we are fully provisioned with food and carry warm and cold weather clothing as both the begining and end of our return trips are in cold weather. I believe this puts us in the "heavily loaded" category.
In 2008, we extended the hull (see pdqforum posting) to cope with the extra weight, etc.
Engine MAX. is now about 3450RPM (or 90% of rated engine max. of 3800RPM), giving a max. speed of about 14.8kts. We run at 3100RPM from New York to Cape May, on the outside but otherwise we prefer cruising in the "slow lane".
I am happy with all the changes related to the props. and hull extension. We run quietly and efficiently.
Engineers are accused of always trying to "improve" things. As a retired mechanical engineer, I plead guilty, but one needs some excitement in retirement.
Hope I fully answered your question.
Cheers,
Frank

[duetto]

frank,

thanks for the info. couple of fup questions: 1) assume 17knots @ 1750 rpms is a typo. 2) what are "skewed" props? 3) what is max rpm that you can reach with 17x13 ?

[Kama Kat]

John,
1. Yes, a "typo", 17.2kts at 3750RPM
2. When the contour of the prop blade is not symetrical but swept back, it is "skewed". This causes radial sections of the blade to enter the water sequentially. This helps reduce prop. vibrations, making for a more quiet operation.
3. 17"X13" props allow Kama Kat to go up to 3450RPM max. in fully loaded condition with full bimini enclosure.
For more info. on props, I would recommend the Propeller Handbook by Dave Gerr, naval architect.
Another thought: our type of engines are not designed to be operated at their max. RPM for longer than about one hour ....good to move quickly in an emergency. Prolonged or continous operation is not advisable beyond about 80% of max. RPM (3040) ......on a series of day runs, say 3100RPM. So, the engine speed range from 3100 to 3800RPM is little needed for pleasure cruising. With our 16" props, the engine had much more power available than we could use, at and below 3100RPM ......hence, we increased prop. diameter. We achieve about the same hull speeds now at 100-150RPM lower than with the 16" prop. Hope this helps.
Cheers,

[Kama Kat]

Hi Dick,

I would like to bring to your attention the topic of "advising on options" originally posted on this forum back in Sept. 2004. I added my comments there in Jan. 2005, discussing the four bladed props.
Yes, it is the props that generate the noise, by vibrating the hulls like a drum. If I were you, I would not walk, but run, to my prop supplier for an up-drade to four blades.
Cheers,
Frank

[DickTuschick]

Hi folks,
I have information on the 4 blade prop upgrade:
We have been able to arrange a "quantity" purchase and therefor get a special discount on the props.
For the owners with 100hp engines the new props would be Michigan 17X14 LH/RH 4 Blade DQX, Normal cost $746 each, our cost $594 plus shipping to your location. I am still waiting on a delivery time quote, (Michigan Wheel is shut down for two weeks this month) but it will be at least 4 weeks before they are available.
They do not have a price for the 75 hp engine size yet as this size prop is not a catalog item and they had to get a special quote on price and delivery.
I already have two owners who would like to upgrade and if anyone else would like to jump on board please e-mail me at Dick@rhumblineyachtsales.com.
I will post the information on the 75 hp props as soon as I get it.
Safe cruising!

[Kama Kat]

Dick,

Just a word of caution when buying off-the-shelf four bladed props.
The relatively closer spacing of the blades (as compared to three blades) opens the potential of harmonic vibrations to be induced in the blades by the trailing edges' vortecies, causing a laud "singing" noise at various RPM .....varies with prop.(the more blades on a prop. the higher the risk of annoying "singing" noise)
Suggest you ask for "anti-singing-treatment" of the trailing edges on your new props.This was included in the price on my props. Effectively, they will grind off the knife-like, thin, trailing edge .....best done by supplier to maintain prop. balance.
Cheers,

[DickTuschick]

Hi Folks,
Finally....here is the info on the 4 blade props for the 75 HP engines.
H&H propellor is coordinating this whole issue of props and I have found them most helpful and supportive.
The US supplier for them was not interested in developing the patterns necessary to produce the smaller props. Their second supplier, an oriental firm is willing to make the pattern, identical in design to the props for the 100's (but smaller), but only if we can give them an order for 5 or more pairs. The cost delivered to H&H would be $562.00 each and delivery would be 10 to 12 weeks. As part of the deal H&H will hand finish (anti-sing) both edges and supply a MRI report with each prop. At this point I have one firm order and two more people voicing interest. If I am able to get the five firm orders I will place an order immidiately. Please contact me directly if you would like to order a pair. dick@rhumblineyachtsales.com.

[DickTuschick]

Hi Folks,
Just a quick update. as of today we have ten orders in for 100hp props and only two folks requesting props for the 75 hp. We need a minimum of five to place the order.
H&H has also informed me that a price increase from Michigan prop on the 100hp props is expected any day and they have no idea how much it will be, but it will not apply to any orders already submitted.

[jim]

The benefit of the four blade props seems impressive. Does anyone have any experience with the addition of the Soundown tiles and/or the Aqua drives to the four blade props? Do they contribute much more to the sound and vibration reduction of the four blade props or is the reduction so great from the new props that the tiles and Aqua drives don't add much benefit.

[DickTuschick]

Hi Folks,
Last friday we launched HERON with a set of the new DX 4 blade props. WOW....same improvement I saw on Cat's Away when I seatrialed her. Basically same RPM/Speeds.
Last summer we put about 2000 miles on her and now with the new props she is like a totally different boat. The improvement is remarkable. I actually got another 75 to 100 RPM at the top end and about 3/4 knot of top end boat speed.

We got the minimum 5 orders for the 75 HP version and that order has gone in to the factory.

12 orders have now gone in on the 100hp version.

I will be talking more about the props at the Owners Rendezvous this weekend in Stuart.