Fuel Burn of Twin Suzuki DF300’s on a 28 Foot Fiberglass Boat

ship happens said:
MpG is maybe useful for some however it's not an accurate representation for a marine traveling vessel for several reasons. It's not used and will make things more complicated.

That's really good numbers with a 25ft boat with a single 300. I'd say you'll never do better than that.
Click to expand...
I agree that there are other factors like tide/current and wind that create a gap between SOG and SOW when discussing marine travel. I was just demonstrating that in my case, 9 gph and 11 gph could be shown to be equal in efficiency of fuel burn by expressing it in mpg.

I am very happy with my numbers but I am in a much smaller boat than the ones discussed on this thread. My numbers for my single F300 are useful for comparison with twins though. Your example of 10-11 gph at cruising speed (3800-4200 rpm) is pretty much bang on for a 300 hp outboard motor. So when conditions have me getting 2.6-2.8 mpg, at 11 gph a boat about twice the size with twins is burning that same amount of fuel per engine or 1.3-1.4 mpg and 22 gph combined.
 
Squire said:
I agree that there are other factors like tide/current and wind that create a gap between SOG and SOW when discussing marine travel. I was just demonstrating that in my case, 9 gph and 11 gph could be shown to be equal in efficiency of fuel burn by expressing it in mpg.

I am very happy with my numbers but I am in a much smaller boat than the ones discussed on this thread. My numbers for my single F300 are useful for comparison with twins though. Your example of 10-11 gph at cruising speed (3800-4200 rpm) is pretty much bang on for a 300 hp outboard motor. So when conditions have me getting 2.6-2.8 mpg, at 11 gph a boat about twice the size with twins is burning that same amount of fuel per engine or 1.3-1.4 mpg and 22 gph combined.
Click to expand...
Well I can't take credit for the numbers, as I'm just teaching you guys what I've learned being in the industry for too long. Those numbers are from the OEM engine manufactures engineering departments. Engines burn what they burn and now days, like I've said in other posts on related topics, with modern injection these engineers know exactly the fuel duration and volume for whatever burn they are trying to achieve for their specific design. Now that being said, fuel is fuel and there is only so much energy in fuel. More hp means more fuel. Period. Can only get so much efficiency from design to design and the last 20 years have basically maxed that out almost. With newer designs coming out they are barely splitting hairs getting more power from less fuel burn if that makes sense. We're miles ahead from where we were 20 years ago. It's all fun stuff
 
Ill add these bigger engines seem to like the 3900 to 4400 rpm range as thats seems to be the "sweet" spot for my boat it likes it at about 4200 rpm 25 to 27 mph and thats about 48 ltrh or 9.5 to 10 GPH if i bump it up im crusing at say 4500 ill do 30 mph and 12 GPH rougly BUT its also a duo prop which make a big differnce too for less fuel burn
 
salmonkiller01 said:
But he has 100hp more. The Verado outboards were extremely efficient. How about engine height have you checked to ensure you’re at the right height @Sharphooks ?
When running on plane cavitation plates are not buried?
Click to expand...

Good point on engine height. I was mulling that over. I just took delivery of the boat and have only run it solo so I’m feeling things out. Need to get someone on the boat to see where the cav plates are underway. I did notice a lot of commotion off the stern at 4,000 RPM (spray)...of course I’ve got a full fledged ghetto of transducers hanging off the transom so there’s that...but yes, I need a separate pair of eyes to see how the Suzukis look, though I just remembered there’s a YouTUbe vid of the boat that was produced after the former owner took delivery... I’m thinking wake looks pretty clean and outboards seem at the right height (best seen at the very end of the vid)?


 
Sharphooks said:
Good point on engine height. I was mulling that over. I just took delivery of the boat and have only run it solo so I’m feeling things out. Need to get someone on the boat to see where the cav plates are underway. I did notice a lot of commotion off the stern at 4,000 RPM (spray)...of course I’ve got a full fledged ghetto of transducers hanging off the transom so there’s that...but yes, I need a separate pair of eyes to see how the Suzukis look, though I just remembered there’s a YouTUbe vid of the boat that was produced after the former owner took delivery... I’m thinking wake looks pretty clean and outboards seem at the right height (best seen at the very end of the vid)?


Click to expand...
Worth checking on engine height, you never know. Nice rig
 
ship happens said:
Ohh wow. You could knock that down a notch and get better cruising speed.
Click to expand...
I put a pic of the numbers on last post. I usually run around 4000 to 4200 but the 3800 reflects the lowest burn and still stay on step without loading. I'm running the 17's right now. I've thought about the 16.5 xp's but hey....I've made my bed. Its only another 2k for another set 🤣
 
BC Coast Pilot said:
I put a pic of the numbers on last post. I usually run around 4000 to 4200 but the 3800 reflects the lowest burn and still stay on step without loading. I'm running the 17's right now. I've thought about the 16.5 xp's but hey....I've made my bed. Its only another 2k for another set 🤣
Click to expand...
That would slow you down and give you more WOT RPM.

I know what you mean though. I've probly got a few grand in props on the wall that for for my own projects that didn't make the cut
 
Sharphooks said:
Cavitation plates appear to be just even with bottom of transom?

View attachment 90976
Click to expand...
That's a stepped/raked pod. Looks like a PDR pod. So yeah the engines are too low. Rule of thumb is 1.5 inches up per foot of setback. However in this case you could ease that back. I would start with 3 inches above the bottom V and see how it goes into a turn.
 
Last edited:
ship happens said:
That's a stepped/raked pod. Looks like a PDR pod. So yeah the engines are too low. Rule of thumb is 1.5 inches up per foot of setback. However in this case you could ease that back. I would start with 3 inches above the bottom V and see how it goes into a turn.
Click to expand...
I can’t see the bottom line of the pod so I can’t tell if it’s raked or not but if it is I concur with Ship Happens. I had to add wedges and raise the main one hole to get the best out of my rig.
And yes, that is a beautiful boat!
 
ship happens said:
That's a stepped/raked pod. Looks like a PDR pod. So yeah the engines are too low. Rule of thumb is 1.5 inches up per foot of setback. However in this case you could ease that back. I would start with 3 inches above the bottom V and see how it goes into a turn.
Click to expand...

Thanks for that, Ship...but a bit more clarification:
I would start with 3 inches above the bottom V and see how it goes into a turn.
Click to expand...

Not sure I understand 3” above bottom V: what are you measuring— bottom of skegs?

Here’s a different angle so you can see the PDR bracket how it relates to the bottom of the transom/ drain plug

Also, I was told WOT is 6,200 (!!)—-I haven’t had water conditions to test but isn’t that a bit on the high side? My last Seasport had twin DF200’s —WOT was a bit under 6K but they had 16x21.5” props—-these DF300’s have 16x18.5”

4135462E-A5A0-4B7A-BAFE-0F6B99DB1A4D.jpeg
 
Last edited:
You must log in or register to reply here.
Back
Top