340 SDB Planing

dahboat

New Member
Nov 1, 2005
1
San Francisco
Can anyone tell me the speed at which my 86 340 Sedan Bridge will plane? Also, at what RPM does the carb secondaries start to kick in on the Merc 454s? Thanks
 
Fuel Consumption Question

I think this is going to be subject to weight onboard, sea conditions, build up on the bottom, props, etc. I am giving serious consideration to adding a fuel managment system to help me see the secondaries open. Hopefully it will pay for itself.

Kevin
Weekend Mistress
Richmond VA
 
We run our twin 7.4s around 3400 RPMs. If you pay close attention you can hear the 3rd and 4th barrel kick in.

You may want to invest in a fuel flow meter, like a Floscan if this is a concern of yours. They pay for themselves in one season if you boat a lot.
 
Not sure about sedan bridges. i think they need more speed because more weight on the same hull square footage.

Sprot Cruisers and Sport Yachts usually plane around 20 mph, but really need 24 to 28 mph to plane "nicely"

The prop pockets in SR inboard hulls really, really kill planing performance and make the boats seem even more tail heavy than they are already.
 
hi alex
i find that i stay out of the secondaries at or below 3250 rpm. that keeps my speed at a hair under 19mph (17+ with a stiff headwind) and gph at around 26 total. i think the specs on our boats are different. i am 12.5' wide and 16500lbs dry.

i believe that prop pockets AID in planing. that is the advantage they have - they tend to keep the shaft angle lower so thrust is directed more outward than downward. this gets you up on plan faster and decreases your running angle.

when i first got this boat, i think i recall being able to hold plane at about 13 mph. boat was dragging a LOT but the wake was flattened out.
 
rondds said:
hi alex
i find that i stay out of the secondaries at or below 3250 rpm. that keeps my speed at a hair under 19mph (17+ with a stiff headwind) and gph at around 26 total. i think the specs on our boats are different. i am 12.5' wide and 16500lbs dry.

i believe that prop pockets AID in planing. that is the advantage they have - they tend to keep the shaft angle lower so thrust is directed more outward than downward. this gets you up on plan faster and decreases your running angle.

when i first got this boat, i think i recall being able to hold plane at about 13 mph. boat was dragging a LOT but the wake was flattened out.

Good points ... I don't know anything about bridge boats and just heard from other boaters that prop pockets are reducing draft, but kill planing performance because the hull does not provide a uniform v-hull surface in the aft. The center section slices the water and pushes it outwards instead on the boat upwards. I know that my inboard 340 is feeling veeery tail heavy and more so than my previous 26 foot cruiser. I understand you comment about prop angle, but a steeper prop angle actually helps planing, that's why stern drives tuck under when trim is all the way down. It pushes the boat up. Anyway, your points are well taken. I run best between 3400 and 3600 rpm and 27 to 31 mph.
 
Like Ron said, just above 3200 rpm the sound from the carbs will start to get louder and you will feel a tug on your wallet. :lol:

Ron, the actual speed was 12.5 mph that you were able to hold plane (from memory) and about 2400-ish rpm. Darn wake was huge!!!!
 
Mark:
i dont want to hear another peep out of you until you get a signature pic UP. if you're too lazy, give my your password and i'll get it up for you . then you can change your password so i dont hack into your posts and get you evicted from these-here boards!
:smt024
 
If you're offering... I'll take you up... :grin:

Check your home email.
 

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