an interesting prop debate. Torque increase with the same prop?

[Hoist]

Being a hoarder of green engines a few years ago I acquired a scrap engine from an identical boat to ours.

Our boat has a VP MD2020, coupled to a 120S with a 16x10 Eliche radice folding prop.

The scrap engine I got was a VP2030, coupled to a 130S with a 16x10 Eliche Radice prop.

Feature	Volvo Penta 120S	Volvo Penta 130S
Gear Ratio	2.2∶12.2 colon 1 2.2∶1 or 1.66∶11.66 colon 1 1.66∶1	2.47∶12.47 colon 1 2.47∶1
Propeller Speed	Higher RPM	Lower RPM
Torque	Lower torque	Higher torque
Engine Suitability	Older, slower-revving engines	Modern, higher-revving engines (e.g., up to 3,600 rpm)
Propeller	Needs a propeller matched to the 2.2∶12.2 colon 1 2.2∶1 or 1.66∶11.66 colon 1 1.66∶1 ratio	Needs a propeller matched to the 2.47∶12.47 colon 1 2.47∶1 ratio

I am now changing my engine for an MD2030 but retaining the 120S

My reckoning is that the MD2020 was very over propped as max revs were around 2600 on a good day!

Am I missing something huge?

Silette quoted me for a 16x13 prop but I think I would like to try the original 16x10 to see what happens.

 

[Tranona]

Being a hoarder of green engines a few years ago I acquired a scrap engine from an identical boat to ours.

Our boat has a VP MD2020, coupled to a 120S with a 16x10 Eliche radice folding prop.

The scrap engine I got was a VP2030, coupled to a 130S with a 16x10 Eliche Radice prop.

Feature	Volvo Penta 120S	Volvo Penta 130S
Gear Ratio	2.2∶12.2 colon 1 2.2∶1 or 1.66∶11.66 colon 1 1.66∶1	2.47∶12.47 colon 1 2.47∶1
Propeller Speed	Higher RPM	Lower RPM
Torque	Lower torque	Higher torque
Engine Suitability	Older, slower-revving engines	Modern, higher-revving engines (e.g., up to 3,600 rpm)
Propeller	Needs a propeller matched to the 2.2∶12.2 colon 1 2.2∶1 or 1.66∶11.66 colon 1 1.66∶1 ratio	Needs a propeller matched to the 2.47∶12.47 colon 1 2.47∶1 ratio

I am now changing my engine for an MD2030 but retaining the 120S

My reckoning is that the MD2020 was very over propped as max revs were around 2600 on a good day!

Am I missing something huge?

Silette quoted me for a 16x13 prop but I think I would like to try the original 16x10 to see what happens.

You have those ratios the wrong way round and your table does not make sense. The 120 is 2.47 and the 130 is 2.21. This is because in almost all cases except a small number of 20X0 engines in 2005 the 130 is used on the D1 engines which max at 3200 instead of 3600. This means that the shaft speed is more or less the same at around 1450. So if you match a 2030 to a 130 (as I did on my Bavaria 37) you get a shaft speed of 1630 which means you need a smaller or lower pitch prop. Volvo are pretty good at matching engines to reduction ratios on small engines, aiming fpr shaft speeds of +/-1500 which is the optimum for the sort of boats the engines are fitted to. With shaft drive they offer options for when the engines are fitted to for example heavy workboats but saildrives are fitted almost exclusively to sailboats and the leg means there are effectively no restrictions on propeller diameter and variations in displacement can be met with the range of different diameter 2 and 3 blade propellers.

However your combination of 2030/120 is correct and 16*10 is the right size 2 blade. or even a 16*11

You are right your 2020/120 is way over propped - it should be a 15*10

 

[Hoist]

You have those ratios the wrong way round and your table does not make sense. The 120 is 2.47 and the 130 is 2.21. This is because in almost all cases except a small number of 20X0 engines in 2005 the 130 is used on the D1 engines which max at 3200 instead of 3600. This means that the shaft speed is more or less the same at around 1450. So if you match a 2030 to a 130 (as I did on my Bavaria 37) you get a shaft speed of 1630 which means you need a smaller or lower pitch prop. Volvo are pretty good at matching engines to reduction ratios on small engines, aiming fpr shaft speeds of +/-1500 which is the optimum for the sort of boats the engines are fitted to. With shaft drive they offer options for when the engines are fitted to for example heavy workboats but saildrives are fitted almost exclusively to sailboats and the leg means there are effectively no restrictions on propeller diameter and variations in displacement can be met with the range of different diameter 2 and 3 blade propellers.

However your combination of 2030/120 is correct and 16*10 is the right size 2 blade. or even a 16*11

You are right your 2020/120 is way over propped - it should be a 15*10

I did think that table was weird! Finally I've found something that google AI is wrong about!

Thanks for the constructive feedback. The boat never should have had a 2020 in it but they get it wrong sometimes

 

[Hoist]

Well I didn't see that coming. The 2020 has a 4 bolt flywheel but the 2030 has a 6 bolt. I'll just be reusing the original 2030 one with the output spline part swapped over. I quick check of the depth should alleviate any concerns. The backing plate where the shaft box bolts onto has the identical part number to that of the saildrive box so I am very confident with the swap.