Yammaha 100hp

[Little Hooker]

Guys ive jus been readin the site on speeds of different boats and etc.

And it seems to me that in boat seems abit slower then some others.

I have a 5.3 alloy boat with a 100hp yammy carbi 04 model.

On the water at full throttle im peaking at 5700rpm at 62kph at the highest ive seen or most times it would be sittin on 60kph. Does that sound right too anyone??

Recently i pulled out the floor boards and see how big that petrol tank was it calculate out to be 70ltrs (i hope i did my maths right). I wanna take the boat off shore soon but not sure how much kms i would get out a tank. Anyone willing to guesss on what the yammy could get on a 70lt tank???

[Beaver]

We have a 5.3 quintrex with yam 100hp 4 stroke. Max we can get it up to is around 65kph

As for how many litres out of tank I have no idea, we can get 4 trips out of a tank fishing the harbour and around the coast...

Edited February 14, 2008 by Beaver

[Boban]

Its not that difficult to work out your fuel consumption if you are prepare to take some notes.

Before you go out, fill up the tank completely. Then travel everywhere you possibly can at 4000 rpm. Do some set runs where you know the distances. Then so some basic maths. You will get a rough idea of how much your boat motor will consume.

There are however many variables to consider, especially when traveling outside the heads. You will obviously consume more in rough conditions and winds that are against you.

The other option is to buy a fuel computer from Navman. Not that expensive especially when you already own a sounder or GPS from Navman.

[Little Hooker]

Doin the maths wouldnt be that hard but the tacho on my boat doesnt seem to be reading right! every time i go out i always fill her up to full but the tacho would never read full bars the most would be about 4 bars which say its half full. So its hard to tell how much is left in the tank.

Fuel computer from Navman sounds like a good idea but i dont own a navman..

[Boban]

Doin the maths wouldnt be that hard but the tacho on my boat doesnt seem to be reading right! every time i go out i always fill her up to full but the tacho would never read full bars the most would be about 4 bars which say its half full. So its hard to tell how much is left in the tank.

Fuel computer from Navman sounds like a good idea but i dont own a navman..

You don't rely on the gauges mate. As soon as you finish your boating, you go to the petrol station and fill her up. That way you know exactly how much you have used.

The fuel computer is a separate system comprising of a sensor that can be connected to either a fuel computer (which is a simple gauge with two buttons) or to a Navman sounder or GPS. They give you a reading of fuel flow, fuel used for the trip and total fuel used.

But like I said, with a bit of patience and note taking you will get a pretty good idea of what you can do. Another option is to take one of those plastic fuel containers with a pourer just in case you run out of fuel. A 10L container should do the job. Just make sure you use the fuel in the container regularly.

[Josh88]

Hi mate,

For fuel figures i can't help you at the moment, but performance wise i have a mate who has a 100hp yamaha 4stroke on a 5.5m alloy boat and thats top speed is again 65kph. We are getting our new boat tomorrow which is a triumph 170cc with a 75hp mercury optimax and the dealer says they've had previous ones with the optimax up to 47-48mph which is about 75-76kph.

Cheers

Josh

Edited February 14, 2008 by Josh88

[Flightmanager]

What exactly do you want the boat to do ? If you are pulling skiers out of the hole , then a smaller pitch prop will give you the torque you require , but at the expense of top end speed. If you are after top end speed , then a larger pitched prop will give you a better top speed , but the engine will have to work harder to get you onto the plane.

If your needs are somewhere in between these two extremes ( and I think that would be most of us ) , then most of your time would be spent travelling at between 3000 - 4000 RPM. Being a carb engine , your fuel efficiency will not be as good as a comparable DI engine ( Optimax , Etec etc ) . Likewise , the injected engines produce a bit more power than their carburetted predecessors , so making a comparison between the two is really not valid. Likewise , comparing a 100HP 4 stroke with a 100HP 2 stroke will give 2 very different readings . Make your fuel calculations in your boat , with your engine .

Another consideration is the type , weight and size of your boat. This will affect your speed and fuel consumption.

To get an idea of your fuel consumption , fill the tank. If you have a log function on your sounder , it will tell you how far you have travelled. As you are intending on going outside , doing the test in calm water is really not going to give you an accurate prediction of your fuel consumption in outside conditions. On your return , fill the tank , and divide the number of miles travelled by the number of litres used. This will give you a NM/l reading. You can of course use whatever units of measure that suit you , but as you buy fuel in litres , I suggest that you use that unit.

For example , my boat (75HP ) uses 1 litre for every 2NM travelled. So , a days boating in average conditions of 20NM , would consume about 10 litres of fuel. As I have a 30 litre tank , my range on that tank ( given the same conditions ) would be 60 NM. If , however I was navigating in a heavy swell , or running into an oncoming wind or tide , I would adjust this figure to about 1.0 litres / NM . This would give me a small reserve as the actual figure may only be .75l/NM . A 10 litre emergency supply is a good idea to carry on a longer journey , just in case.

Ross

[Little Hooker]

Ahhh i get it now. Will put this all in to pratice if this sickness of mine will go away for the weekend

I only use the boat for fishing and jus the odd cruising around. Not really fuss on the speed i jus want to know what the motor is capable thats all.

Not to say im wrong or right but wouldnt a 100hp carbi or efi motor still be the same at top end?? As they are rated at the 100hp from factory?? fuel consumption and respones out of the hole would be the only advantage over the 2 types?

[Flightmanager]

Not necessarily , even though both motors are rated at 100HP , their gearing and prop sizes will play a large part in final speed . Also , different manufacturers have different standards when rating an engine , ie Evinrude rate their engines at the lowest possible output , so a 100HP engine may well develop 108 - 110 HP at the prop. Other manufacturers rate their horsepower at the maximum it will produce.

Ross

[Little Hooker]

flightmanager thanks for sharing that with me.

I keep that in mind when one day i move on to the efi motors.

Edited February 14, 2008 by Little Hooker