30 to 40 tohatsu

[jerson]

i've got a 2 cyl 30hp tohatsu on the back of a 4.3m tinnie which travels at max 40klms per hour. If i up grade to a 2 cyl 40hp tohatsu what should i expect top speed to be.

[kilo11]

too blood quick

[lippa]

prop the one ya got, it will go heaps better

[krazyfisher]

all depends on your hull weight etc but I had a 40 2cyl tohatsu on a hornet 435 and it did 56kph with gear and two on board.

[jerson]

The boat is a seajay seeker.
Lippa, when u say prop the motor, do u mean a new prop if so what make would you recommend at what approximate cost.

[Fishin_Dan]

Jerson - Give the boys at Solas Props a call and have a chat to them. They will be able to give you the best indication.

MUCH cheaper than going to a 40HP.

The other thing to think about it is what is the max rating on your hull for an outboard? Does it allow the 40HP to go on? Won't be as big an issue for the actual boat, but insurance won't cover you

[jerson]

Dan, the reason for my original post was when I bought the boat new the dealer told me it was rated to 40 hp but this wouldn't be any faster than a 30hp but with more torque. This didn't sound right at the time. The dealer was an agent for yamaha and I thought the 30 & 40hp yammy may have been out of the same block as is the 25 & 30hp tohatsu.
Thanks for your input.

[Dezmo]

Hi,

I have tried the 30 and 40 hp tohatsu (badged as mercury lightweight) on my boat a quintrex 420 dory. Have not measured the speed but would imagine i get better than 40km/hour WOT.

The 40hp has a lot more torque, it seems much smoother (3 cyclinder) and does not get the annoying high pitched scream of the 30hp. From memory the 40hp was not much quicker than the 30hp but i could probably improve mine with a new prop also. The difference in speed between the 30 and 40hp would obviously be more noticeable with a heavy load.

Mine is tiller with manual everything and the extra weight of the 40hp is substantial and certainly a down side.

Apart from the prop, have you got the engine set to the correct height on the transom. While it sounds obvious, have you experimented with trim?

[fishn-ads]

I have the Tohatsu M40c on a Stessco 4.2 catcher it's a bit lighter then yours WOT well I don't know because I have the standard prop. she cavitates with light loads. What I do have The lady abit under 50kg, me 105kg, 1/3 full 80lt esky, all gear, 30lts fuel = 54km/h bout 3/4sh trottle before she cavs (fast enough). Two mates 120kg and 85sh? me 105kg same gear = 44 km/h WOT no cav.

As far as new prop. if it's max. revs WOT loaded which you can easily tell with GPS. WOT back off the trottle slowly watch how much the boat slows? Most dealers have a pretty good idea when it comes to Prop. size for boat/load appication. The 30hp (13lt/hr) on the seeker I think is going to be pretty cheap to run compared to the 40hp (17lt/hr) there alot thirstier.

That said 23-24kt is a top crusing speed in a tinny of that size, much more on anything other than glass and you need a kidney belt.

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[wayne_cook]

I had a 25 toh.on a 4.3 quinnie and went to the 40 2cyl toh top speed was about the same but I had more grunt for getting on the plane. I was mainly beach launching and for running up the beach with a load of fish u need grunt and this is where the 40 made the difference also I didn't notice much fuel difference.

The 3 cyl I'm sure would give u more speed but a fairly big jump in weight.
Weight was a factor for me that's why I went the 2cyl