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AD41D Max RPM amp prop size for stern drive

seaeagle

New member
"Hello,

I'm a new membe


"Hello,

I'm a new member with a new boat with a AD41D engine. I do not know when it was manufactured, but suspect 10+ years ago. I just got a new boat a 25' Davis Rock Harbor with the AD41D coupled to a volvo-penta duo prop stern drive DP-D1 1.78 with propeller size #4 (Aluminum).

I don't have the engine manuals yet and would like to find out the Max RPM allowed for this diesel. I'm trying to determine the correct prop size for the motor - vessel - outdrive setup. I did search the message boards and I could not find a similar post.

Help with the Max RPM and prop recommendations would be great.

Thanks,

Steve"
 
"Most people shoot for 3850 -

"Most people shoot for 3850 - 3900 WOT when the boat is fully loaded (full fuel, water, people, tackle etc) The prop set is determined by the weight. Make sure the air filters etc. are clean.

Fill the boat and take it for a test. Your most accurate results for rpm will be made with a phototach. Once you know the current rpms, we can help determine what prop set you will need.

Good luck with the new boat. Nice boat and engine package. Get the maintenance records from the former owner and don't forget to maintain the outdrive."
 
"Testing out which prop might

"Testing out which prop might be a bit of a hazzle on the DP diesels.
A lot of the props might give You the allowed max rpm, about 3800. You may have to keep on testing until You find a set that gives You only 3600 and then go down one number.
Next is to be sure You have a set that makes the boat go in planning without too much of problems. The turbo and power only kicks in at about 2600. The 41 in the stern of a 25 ft boat might be a bit aft-heavy. Often a set of trim-tabs may be needed, or You will end up with a set that over revs at top speed."
 
"Bill & Morten,

Thanks


"Bill & Morten,

Thanks for the replies. I was planning on getting a phototach to make sure my dash tachometer is calibrated correctly with the engine rpm.

My boat is a bit aft heavy with the 41 & 130 gallons of diesel fuel. She is meant to carry a lot of weight so I'm going to have to add ballast forward to get her trimmed correctly. I do have trim tabs so that helps.

On Friday I took off the rear propeller only to find that I didn't have the correct tool (the socket-sleeve) device to get the retaining nut off for the forward prop. Once that is done I'll talk to a prop shop also.

Appreciate your tips,

Steve"
 
"No need for a special tool fo

"No need for a special tool for the forward nut. Just remember to unsecure the tabs!! Then knock it counter with a punch, but carefully! Adding weight for balancing is not always a good solution. Test first without ,by using the tabs and trim if You got the 290 drive?
I once had a 28Ft Finnspeed with twin AQAD31A/290DP -2.15:1. With the fuel tank of 400 liters just in front of engines. With a little tweaking of smoke limiters etc, I ran A5 and above 30 knots at full speed with a displacement of 5.5Tons!"
 
"The outdrive model number is

"The outdrive model number is DP-D1 1.78. The boat had a 7.4L gas engine to start with. I'll try to take the punch approach to carefully loosen the forward propeller nut. Thanks, Steve"
 
"I changed the duo-props from

"I changed the duo-props from an A3 to an A4 prop set. I ran the boat yesterday and at WOT, the rpm topped out and 3900. The boat wan't fully loaded but it was close to how I'll normally run her so this is the correct prop set for my vessel with the AD41D."
 
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