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Old 09 December 2018, 19:33   #1
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Country: USA
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Make: Bombard Commando C4
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MY Top Speed Is Not So Great, Bombard C4 With 50hp

Bombard C4 with 50 hp Tohatsu

33 mph/53 km/h at 5800 rpm with just me on board.

I was hoping for at least 40 mph/64 km/h

I have it set up with jockey seat, and a hydrofoil and a Hydraulic transom plate for swallow water use.

I am running with 15 pitch prop at 5800 RPM's.

Is this normal, it does handle good, bow stays down and it plans in 1 to 2 seconds.


I have adjusted the trim and motor height and my top speed is still 33 mph/53 km/h.
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Old 09 December 2018, 20:18   #2
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I do understand the some Zodiacs have speed tubes and that lifts the boat out of water and helps with a faster speed but I at least thought a 50 hp on a Bombard C4 would be faster than 33 mph/53 km/h

Or is this about normal..
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Old 10 December 2018, 04:50   #3
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Any videos of it going along? and any pictures of the prop?
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Old 10 December 2018, 11:41   #4
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Hydrofoils reduce speed due to drag.

Videos would be helpful, especially ones showing your wake.
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Old 10 December 2018, 13:51   #5
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Quote:
Originally Posted by office888 View Post
Hydrofoils reduce speed due to drag.

Videos would be helpful, especially ones showing your wake.
When I was putting the boat together I installed the hydro foil before the 1st time using the boat so I don't know what speed might have been lost, I have heard from others its only 1 to 2 mph but many have said no mph lost, I have a auto jack plate so when running I can raise motor to get the hydro foil out of water just before the prop sucks air and it does increase my speed but that would also be the same without a hydro foil, the hydro foil pops the boat on plane at very slow speed and keeps it there so I cant see much mph lost from that, maybe when the weather here warms up I will get a video but not sure why this would help.


Would like to hear from others with similar boat and 50hp what is your top speed.
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Old 10 December 2018, 14:12   #6
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Its the fabric hull I presume. It just isn't as slick on the water. I have a Zodiac Futura MK2 with a Etec 60hp. Yea, I know its a 40hp recommend and a 50 max but the 60 was the same engine with 60hp software and was only $300 bucks more, so who wouldn't.
I have two seats mounted to low storage box with homemade stainless tube control mounting. With just me on board I only hit 37mph. 35mph with my buddy with me. Now I get to full speed in just 4 sec but the engine runs at 6000. I debate getting a stainless prop with hopes of dropping revs to 5900 and add a couple mph but I would need to find the prop used so when I find out it didn't help I can flip it with little financial pain.
My Zodiac dealer told me to increase the tube pressure 1/2 a psi. So go from 3.4 to 4psi. He guessed I could get 5 mph more but that sounds like what a prop salesman would promise you to make a sale. Ill try that first but where I boat there is a big temperature change during the day so checking on the pressure is a hassle but a must do when you over pressure.
My prop is a 13.3 17P 3blade - a pull toy prop is a 13" 15P 4 blade. it goes 33mph with two on board and jumps out of the water when you hit it.
The boat is extreamly stable with no sketchiness with the 60HP.
I love my boat
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Old 10 December 2018, 14:37   #7
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Quote:
Originally Posted by pagick View Post
Its the fabric hull I presume. It just isn't as slick on the water. I have a Zodiac Futura MK2 with a Etec 60hp. Yea, I know its a 40hp recommend and a 50 max but the 60 was the same engine with 60hp software and was only $300 bucks more, so who wouldn't.
I have two seats mounted to low storage box with homemade stainless tube control mounting. With just me on board I only hit 37mph. 35mph with my buddy with me. Now I get to full speed in just 4 sec but the engine runs at 6000. I debate getting a stainless prop with hopes of dropping revs to 5900 and add a couple mph but I would need to find the prop used so when I find out it didn't help I can flip it with little financial pain.
My Zodiac dealer told me to increase the tube pressure 1/2 a psi. So go from 3.4 to 4psi. He guessed I could get 5 mph more but that sounds like what a prop salesman would promise you to make a sale. Ill try that first but where I boat there is a big temperature change during the day so checking on the pressure is a hassle but a must do when you over pressure.
My prop is a 13.3 17P 3blade - a pull toy prop is a 13" 15P 4 blade. it goes 33mph with two on board and jumps out of the water when you hit it.
The boat is extreamly stable with no sketchiness with the 60HP.
I love my boat
Well than I guess I my speed is normal than, on the North American thread they have post of people top speed and some with 150 hp don't see much above 50 mph so I guess mine is normal, it does perform very well and does not have any bow rise issues at top speed, when it warms up wee need to meet in Lake Havasu
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Old 10 December 2018, 14:45   #8
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The bigger Hp can't seem to break the 40 mph but it can really help when you add the 4-5 guy to the boat.
Ill post some videos and a pic of my setup once I upload to youtube
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Old 10 December 2018, 15:30   #9
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I would suggest a higher pitch, like 19 or 21 to increase speed.
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Old 10 December 2018, 16:02   #10
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I wouldn't change prop pitch as the one you are currently using already gets you into the max rpm range with just one person onboard. A larger pitch will reduce your max rpm and put more strain upon the engine, especially if you load the boat with more than just yourself.

Personaly I've never liked using any kind of foil on outboards, partly as they wave your warranty rights on new outboards over this side of the pond. I've also had some diverse dangerous experiences using them in very rough weather on standard mono hulls.

Prop shape can make some difference as can extra cupping of the blades. Engine mounting height can also effect speed but I doubt you will reach that 40mph from simply raising one or two holes but you will gain speed.
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