Horse Power And Speed

[Narralakes]

Have no money to buy a bigger boat, so thinking about maximizing speed by buying the biggest possible motor for the tinny I have. It goes like this,

3.5 metre punt

At the moment has a 5 hp Yamaha

Enquired about a bigger motor, guy at the boat shop said max 8hp for my boat and said it would go twice as fast as the 5 hp and he reckons about 20 knots, as the 5 hp pushes at about 8 - 10 at the moment. Reason being, the 5 hp is a single cylinder, the 8 hp is a twin, therefore more power/thrust and as a result speed.

Anyone have a idea on this one? Any comments appreciated.

thanks

Narra

[Guest Jocool]

Sounds valid. It will also give you more torque, which will help in quicker out of the hole times.

[Grantm]

GDAY Narra,

Thats a pretty fair call Id say. Single cylinder motors have very low torque and although rated at 5 hp dont show it on the back of a boat and is no indication of their power. Step up to 8HP and two cylinders and your starting to get somewhere.

Your 8HP will be 8HP on the boat, and will go like the clappers. Ive seen a photo of you Ken on the forum and I reckon youd be 65kg ringing wet ! So if your the only one in the boat ,giddup I reckon the prop will be the only thing in the water !!!. A second body will take a bit off though but it will be great anyway.

Anything with two cyls now has torque and on a 3.5 meter will be perfect.

PS what are you doing with your stuffed motor ?

Cheers :grogon:

[xtosea]

Just wait and get a new boat, it won't add that much value to your boat. I had an inflatable 2.7m with a brand new 15hp on it. Did about 60 clicks. :thumbsup:

[Guest bluecod]

Narra,

We [the office] had a 4.3 heavy duty punt with a 7.5 on it and it got along reasonably well for what it was intended for. When we upgraded to a 15 it went like a scalded cat - fast enough to be dangerous in inexperienced hands - that's with two adults and about 70 kg of survey gear [say 3 adults] add another adult and performance was lacking. Being a snub nosed punt, there was no "hole" for it to climb out of, it just took off.

It was also a lot of fun on glassed out conditions with 1 up if you didn't hit the turns too hard [sideslip]. :happy:

A mate had a 10 foot V bottom Brooker powered by a 7.5 and it got along very nicely 2 up.

Going from a 5 to an 8 on a smaller flat bottom punt, I would imagine you will get good performance 2 up, but a third person would be quite noticeable.

[Ozy]

I looked at upgrading my motor recently. I have a 15hp and wanted extra power but could only go to the max hull rating of 20hp but I couldn't get my head around spending the money for an extra 5hp despite several dealers and people who should know telling me it would make heaps of difference :confusuion:, so I know how you feel .

Edited October 12, 2004 by Ozy

[Pukka]

...ooops wrong thread, ack!

Edited October 12, 2004 by Pukka

[Narralakes]

Thanks everyone, I really appreciate the help that everyone gives on this Forum, its the BEST! :thumbsup:

Seems like the consensus is that an 8 hp will deliver on power and speed for what I want, and sounds better when everyone reckons with 2 it will plane. The 5 hp I have now, it planes with 1, but with 2, I might as well get out the oars.

xtosea - I would love to get a new boat, but the mrs says we've got 4 kids to feed and we cant afford anything else, she's got a point there. so, a compromise is to get the 8 hp for the tinny I have now. She reckons I can think about it in 4 yrs once our number 3 is finished at her primary school.

Grant - someone is having a look at the motor now

Joe - have you got a dealer number for the e-tec motor?

I did enquire with the Tohatsu dealer, they had their 8 hps going for about $100 more. BTW, what is the "hole", is that getting it to the plane??

thanks again,

Narra

[Grantm]

Narra,

'The Hole' is the period your boat is in when trying to get it on the plane. Your old 5hp with two people would have been permanently in this hole i reckon !

BTW Tohatsu motors are top shelf motors -little known fact i think. Perhaps a bit underated. I worked at a Tohatsu Dealer for many years and knew them well. Very solid contsruction, not much that isnt stainless steel.

Cheers

[Narralakes]

Thanks Grant

[Guest Jocool]

I also have a Toey on my boat. Great motors.! :thumbsup: Dunno if the E-Tecs come in such a small size Ken! :confusuion:

[Narralakes]

Thanks Joe,

I might go the yammy as it is a touch cheaper and quality is good.

cheers

Ken

[patl]

I have a 25 Tohastu on my 4 metre Qunnie, it has had the restricter plate taken out of the carbie and is the same as a 30.

Full of gear and live bait tank full, two up, does 30 knots on the sounder - sounders can be notoruiosly wrong though.

This is the second Tahastu, basic, built well and have never had a problem - touch wood.

A mate of mine in Townsville ran a hire boat business and he used Tohastus, as you could imagine life for those motors were terrible yet they kept going. In fact I have seen someone wear a prop away over a weekend.

[tyrone07]

ive got a 12 ft flat bottom v nose punt with a brand new 15 johnson and it flys goes a bit slow with three but just a good boat to fish the esturaies.

[Narralakes]

I was thinking about getting something that size, but the guys at the shop told me the max size engine for my boat would be a 8 hp. I wouldnt mind getting a 10 perhaps, it would probably take off with a 15!