Noob question about twin engine

[psneeld]

I know the reasons why....but for the less technical explanation.....


or in laymans terms... put both engines in gear of many sporty diesel boats...you just about get knocked off your feet....do that with most gassers and its a much more gentle acceleration.


Thus why more often than not, you need some throttle when maneuvering in wind/current.

 

[oscar]

I know the reasons why....but for the less technical explanation.....


or in laymans terms... put both engines in gear of many sporty diesel boats...you just about get knocked off your feet....do that with most gassers and its a much more gentle acceleration.


Thus why more often than not, you need some throttle when maneuvering in wind/current.

Torque, prop size all that.

 

[LarryM]

... put both engines in gear of many sporty diesel boats...you just about get knocked off your feet....

That's for sure. I always ask anyone standing to hold on before I put my engines in gear. I leave them idling and only work the gears. In and out of the slip, just quick bumps is all it takes. Not ideal, but plenty of steering authority.

They idle at ~875rpm, and with the gear and prop combination even requires alternating in and out of gear in fairways and no wake zones.

What a contrast to my previous boat, a Fales 30 trawler Boomarang. Back and fill, back and fill, rinse and repeat . . . .

 

[guy with a boat]

I know the reasons why....but for the less technical explanation.....


or in laymans terms... put both engines in gear of many sporty diesel boats...you just about get knocked off your feet....do that with most gassers and its a much more gentle acceleration.


Thus why more often than not, you need some throttle when maneuvering in wind/current.

Many sportfishers (including my old boat) run between 5 and 6 kts at an idle in gear. I’ve never seen that with a gas boat. The props know because they are driven by a different level of torque at idle speed in most diesels vs. most gassers.

 

[rslifkin]

Many sportfishers (including my old boat) run between 5 and 6 kts at an idle in gear. I’ve never seen that with a gas boat. The props know because they are driven by a different level of torque at idle speed in most diesels vs. most gassers.

Yup. My boat has more idle thrust than most other gas boats I've seen (lower revving engines than many gassers, plus fairly deep reductions and big props). And even then, it's not that speedy at idle. In dead calm water with idle speed set to spec (~680 in forward gear tied to the dock) it does a little over 4 kts at idle, but putting both engines in gear from a stop only gives a small kick, the acceleration isn't quite as instant and violent as some diesels produce.



The highest idle thrust and speed typically comes from fast boats with big, low revving diesels. If a boat does 30 kts, WOT RPM is only 2200 and it idles at 600, it's going to move a lot faster at idle than, say, my boat that idles at 700, but WOT is 4200 and it only does ~25 kts at WOT.