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

[InterMechanico]

@Sharphooks I think he means:
- Use a straight edge laying against the bottom of your hull aligned with each engine to measure the height of the underside of the anti-cavitation plate relative to the hull. Make sure your engines are trimmed to make the anti-cavitation plates parallel with the hull when you take your measurement. Take your measurement at the center point of the anti-cavitation plates.

He mentioned that the anti-cavitation plates should be higher than the hull by 1.5" for every foot of setback from the transom. He also mentioned that it would be alright to try raising the engine 1"/foot of setback to start, eg: raise them 3", by estimating the pod to be 36" long.

If your pod is Not raked upward and carries the profile of the hull backward to the mounting plate, then you would measure your setback from the bottom or the pod mounting plate.

If you pod is raked upward, then you would take the setback measurement from the bottom edge of the transom.

 

[InterMechanico]

That's a nice boat BTW. Beauty. A little Jelly if I'm being honest haha

 

[InterMechanico]

I have mashed up your photo to better see the pod. Does not look like it follows the hull profile. If this is correct, then @ship happens has given you the good advice.
Either way it's good advice

 

[ship happens]

Thanks for that, Ship...but a bit more clarification:


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”

View attachment 90978

Boat builders hardly ever setup outboards properly. Nor do most of them ever prop them correctly. That boat does 6200 rpm because you put 600 hp on a boat that requires much less.

I know that's a PDR pod because Seasport buys them from PDR. This second picture is no good. Take a closer up picture like the first one you posted.

 

[Sharphooks]

That’s very helpful advice, Ship and IM—-I appreciate it. A few boats ago I had a 24 Skagit Orca that had a single DF300 hanging off an Armstrong bracket
It was sluggish in the water, lots of commotion off the stern. I had a welder extend the bracket deeper into the water so the bottom of the bracket was level with the keel of the boat....this had the effect of raising the DF300 up out of the water from the added buoyancy—-it made me a believer in tweaking outboard height to improve performance...night and day difference. This boat comes out of the water next week and I’ll do those measurements for sure

 

[ship happens]

That’s very helpful advice, Ship and IM—-I appreciate it. A few boats ago I had a 24 Skagit Orca that had a single DF300 hanging off an Armstrong bracket
It was sluggish in the water, lots of commotion off the stern. I had a welder extend the bracket deeper into the water so the bottom of the bracket was level with the keel of the boat....this had the effect of raising the DF300 up out of the water from just with the added buoyancy—-it made me a believer in tweaking outboard height to improve performance...night and day difference. This boat comes out of the water next week and I’ll do those measurements for sure

That boat wasn't setup right then. Your new boat isn't either. It's all about engine height. Espciacially with raked pods. That one is raked for sure. In the case of a raked pod, you no longer level the cavitation plate even with the boat or just above. Just like what @InterMechanico explained as well. You raise it up 1.5 inches per foot of setback.

Now you'll be able to choose different props

 

[salmonkiller01]

That boat wasn't setup right then. Your new boat isn't either. It's all about engine height. Espciacially with raked pods. That one is raked for sure. In the case of a raked pod, you no longer level the cavitation plate even with the boat or just above. Just like what @InterMechanico explained as well. You raise it up 1.5 inches per foot of setback.

Now you'll be able to choose different props

Ship happens is right about that. Use the 1” up for every foot back as reference. 36” bracket outboard up 3”. However it is only a reference. My boat with the original Verado was 5” up from bottom of hull My 200 is now 3.5”

 

[Sharphooks]

Not to beat up this horse more then we should, I have to ask: a “raked pod” is an outboard bracket that doesn’t extend sternward at the same level as the keel of the boat?

 

[ship happens]

Not to beat up this horse more then we should, I have to ask: a “raked pod” is an outboard bracket that doesn’t extend sternward at the same level as the keel of the boat?

I can't tell from the pictures if his pod is raked or stepped. However still needs to raise the engine height. Well get to that when we see better photos

Here's a ****** little drawing.

 

[salmonkiller01]

I can't tell from the pictures if his pod is raked or stepped. However still needs to raise the engine height. Well get to that when we see better photos

Here's a ****** little drawing. View attachment 90986

Raked brackets are usually stepped. My current one is and my Armstrong was. Generally they are 3” above keel line and then the motor is 3 inches higher on the bracket than it would be as compared to mounting directly at transom

 

[ship happens]

Raked brackets are usually stepped. My current one is and my Armstrong was. Generally they are 3” above keel line

This is true, except I rank them differently because of the height setback requirements. Raked needs more setback lift. Best to keep things simple in the understanding of this engine height topic.

 

[Squire]

Raked brackets are usually stepped. My current one is and my Armstrong was. Generally they are 3” above keel line

I believe the step is meant to accommodate the original plug.

 

[ship happens]

I believe the step is meant to accommodate the original plug. View attachment 90990

Yep that is a valid point. Sometimes that step can be alot higher. Just depends on the bracket design. I've seen them stepped up 6 inches or more. Really just depends on the fabricator and the boat shape. However the step needs less engine lift because most of them do not completely break free when on plane. Where as a raked pod does break free.

 

[Sharphooks]

That’s very helpful info, Ship....thanks

This was the bracket profile of my earlier 26 Seasport—-based on your drawing, def. a stepped bracket on the Commander—-the manufacturer does use all PDF brackets—-very similar to this one——at least 6” of transom clearance above the drain plug before the bracket attachment point. You can see drain plug just above prop hub of starboard Suzuki

Once I get her on a trailer I can get some pix

 

[gunnerlove]

That's interesting but it's a displacement formula. we're talking planing hulls here.

The fuel burn is physics and the table is clearly labeled "planing Hulls".

 

[InterMechanico]

The fuel burn is physics and the table is clearly labeled "planing Hulls".

All in the details

 

[Fritz]

The fuel burn is physics and the table is clearly labeled "planing Hulls".

What you want to do is get a bigger engine and run it at lower RPM.
For example if I put twin 600hp Mercs on my boat and put 80P props on I can do 95.6mph at 650rpm and by my calculations the engines will actually fill the tanks with fuel!
You and your physics pffffffft!!!

 

[ship happens]

What you want to do is get a bigger engine and run it at lower RPM.
For example if I put twin 600hp Mercs on my boat and put 80P props on I can do 95.6mph at 650rpm and by my calculations the engines will actually fill the tanks with fuel!
You and your physics pffffffft!!!

Ohh man I almost choked on coffee

 

[BC Coast Pilot]

The fuel burn is physics and the table is clearly labeled "planing Hulls".

My apologies, the planing hull bit was obscured on my little phone view.

 

[doug78]

While im running a much smaller boat...moving my motor up two holes completely changed the boat. It came to me mounted nearly as low as possible and running a 15 1/2 x 15 pitch yamaha 3 blade. It now runs a 17 pitch and planes slower than the 15 ever could...cruises right at 4200 instead of 4900 and the steering is much smoother.

Looking forward to seeing where this goes!