volvo tmd40a prop

[O-fishal]

Re: volvo tmd40a prop

You will probably want a 1.95;1 280 with a duo prop lower unit and A4 props if you go to page 5 of the volvo prop guide that I previously posted and look at the AQD40A which is what you motor becomes with the aquamatic sterndrive it is all right there!!!

 

[Maclin]

Re: volvo tmd40a prop

Re: volvo tmd40a prop
"im sorry but i believe you are worng on the ratio part a mechanic gave me this info and my motor is a 140hp and also the mechanic told me that a drive from a 4cylinder has more rotation because of the smaller motor and less rmps and a drive from a 4 is 2.30 to 1 and also thats why a dp drive has a 1.93 to 1 because of the 2 props ahveing a counter rotation if a i am wrong then the expert is wrong im going to look into that info to see i dont know anything aout ratios so "

I am not wrong. The ratio is Engine to Prop turns. A drive ratio of 2.3 means the ENGINE spins 2.3 revoultions to get 1 revolution at the prop. You either misunderstood the expert or you need another one. Based on your last sentence it could be a combination between the two.

DuoProp drives are higher numerically because the duoprop sets pitch make up the "difference". You cannot compare a DP to an SP regarding final drive ratio (at the prop).

You also cannot compare a diesel to a gasoline engine regarding power band in relation to RPM's. TMD40 top RPM is 3,600. A similar HP gasoline engine's top rpm is almost 5,000 rpm. If you go with the 2.3 ratio in a SINGLE PROP drive you will SEVERELY limit your top speed.

The advice on the 280 with DuoProp is correct, the ratio would be 1.95 and propset would be in the A4-A6 range more than likely. That equates roughly to 19-23 pitch.

 

[RogersJetboat454]

Re: volvo tmd40a prop

Re: volvo tmd40a prop
"im sorry but i believe you are worng on the ratio part a mechanic gave me this info and my motor is a 140hp and also the mechanic told me that a drive from a 4cylinder has more rotation because of the smaller motor and less rmps and a drive from a 4 is 2.30 to 1 and also thats why a dp drive has a 1.93 to 1 because of the 2 props ahveing a counter rotation if a i am wrong then the expert is wrong im going to look into that info to see i dont know anything aout ratios so "

I am not wrong. The ratio is Engine to Prop turns. A drive ratio of 2.3 means the ENGINE spins 2.3 revoultions to get 1 revolution at the prop. You either misunderstood the expert or you need another one. Based on your last sentence it could be a combination between the two.

DuoProp drives are higher numerically because the duoprop sets pitch make up the "difference". You cannot compare a DP to an SP regarding final drive ratio (at the prop).

You also cannot compare a diesel to a gasoline engine regarding power band in relation to RPM's. TMD40 top RPM is 3,600. A similar HP gasoline engine's top rpm is almost 5,000 rpm. If you go with the 2.3 ratio in a SINGLE PROP drive you will SEVERELY limit your top speed.

The advice on the 280 with DuoProp is correct, the ratio would be 1.95 and propset would be in the A4-A6 range more than likely. That equates roughly to 19-23 pitch.

+1 ^^^^

Sounds like the OP's mechanic was having a bad day when giving advice...

 

[macorre4]

Re: volvo tmd40a prop

ok the prop my my boat is a 15x17 so what should i use and which one is the pitch the 15 or the 17

 

[Maclin]

Re: volvo tmd40a prop

15x17 would be a 15 inch diameter prop with a 17 inch pitch.

(17 inch pitch means the boat would move 17 inches for each rotation of the prop if the water did not "give")

That to me sounds like it is pretty close to ideal for your boat and engine/drive combo.

How fast is the boat going at the 3,000 rpm that the engine cannot get past when trying to plane?
Is the bow of the boat really high out of the water at that point?
Do you have any trim tabs on the boat? If so, do you start out with them all the way down then gradually trim them up?
Does your drive have power trim (a 280T)? If not, what setting do you have the drive trim pin in out on the drive?

 

[macorre4]

Re: volvo tmd40a prop

ok the pin on the drive was on the 2nd one from bottom to top i moved back to the bottom one no the drive does not have power trim yes my boat has trim tabs but have not tried taking off with them down ill try that do u think i should change the pitch and diameter if so what should i change it to

 

[Maclin]

Re: volvo tmd40a prop

My advice now is: Learn more about using the trim tabs before changing props!

They should be down to start off with, then when the boat begins to plane move them up slowly.

In my opinion, if that engine is running is in good condition and in top tune and the prop is in good shape then the boat should be able to plane out with the prop you have, and be able to reach 30mph at top rpm of 3,600.

If it is still struggling to plane even with the tabs helping then maybe a 15 pitch prop would be something to try. A 15 pitch would drop attainable top speed to 27 at top rpm's (3,600).

Play around with this prop calulator and you can see the way that engine rpm, drive ratio, prop pitch and prop slip % are related....:

http://www.marksmarineinc.com/prop_calc.aspx

Typical prop slip in the water is 12-15% at top rpm's.