Mercury 3.5hp 4stroke prop

Whaleoilbeefhooked · 23 July 2023, 13:48

Hi..I'm a newbie at boating and have recently bought a 3.3m sib so I can make some memories with my grandson, while I still can, who is 5.
I've purchased a new 3.5hp 4 stroke mercury and tbh I'm slightly disappointed with it's performance. I wasn't expecting to break any world records but it I get overtaken by rowers on the Dee!
I have seen online and YouTube that it's basically the same engine as the 5hp and 6hp one.
There is also a upgrade kit I've seen that's available in the States that increases the hp to 5hp and the kit also includes a new prop.
If this is the only difference, would I be able to just fit a 6hp carb on it and put an aluminium prop on..has anyone had a similar experience or actually done the upgrade?
Many thanks,
Nick 👍

Steve509926 · 23 July 2023, 13:57

Hi Nick and welcome, others with far greater knowledge than me will be along shortly.
However, what is your 3.3 mtr SIB?

Fenlander · 23 July 2023, 15:02

Welcome to the forum Nick.

Are these inland non-tidal rivers you will be on? From my experience a 3.5hp motor will push a 3m or so SIB to the max legal/desirable river speed. You are just going to make more wash with a 5/6hp and really need an 8/10hp minimum to get on the plane (with light load) and make a worthwhile speed increase... which of course is only needed at sea.

Whaleoilbeefhooked · 23 July 2023, 15:17

I've got a Costco special a Tobin..if it gets used as much as I'd like to think I will then I'll go for the one I really wanted which was the 3.8m Boatworld V airdeck. It was almost twice the price for what seems like not a lot more length..I've already upgraded to this from a 2.6 waveco which after a couple of weeks decided I was to big for the boat lol.

Limecc · 23 July 2023, 18:06

Quote:

Originally Posted by Whaleoilbeefhooked

Hi..I'm a newbie at boating and have recently bought a 3.3m sib so I can make some memories with my grandson, while I still can, who is 5.
I've purchased a new 3.5hp 4 stroke mercury and tbh I'm slightly disappointed with it's performance. I wasn't expecting to break any world records but it I get overtaken by rowers on the Dee!
I have seen online and YouTube that it's basically the same engine as the 5hp and 6hp one.
There is also a upgrade kit I've seen that's available in the States that increases the hp to 5hp and the kit also includes a new prop.
If this is the only difference, would I be able to just fit a 6hp carb on it and put an aluminium prop on..has anyone had a similar experience or actually done the upgrade?
Many thanks,
Nick ��

I purchased the readysetboat kit and it didn't get caught by customs. I'm very pleased with it.

Easier to just get a 5hp carb and alloy prop off ebay. Some have fitted 6hp carb and reported it runs too rich. 4,5,6 hp carbs all have the same venturi size, only the jets are different and the sizes are on the parts lists.

The readysetboat prop was actually a lower (and metric) pitch. I expected the reverse. I've precise details if you want them.

I also changed the decals and branding lol

Whaleoilbeefhooked · 23 July 2023, 18:11

Thank you for your help, it's what I wanted to here.
I'm not after a Bluebird but just want a little bit more top end than I've got.
Thanks again ��

Fenlander · 23 July 2023, 20:58

>>I'm not after a Bluebird but just want a little bit more top end

If you are new to boating do you know your maximum speed on the river is dictated by the length of the boat not the horsepower?

Whaleoilbeefhooked · 23 July 2023, 22:08

Totally get where you're coming from and the speed limit on the Dee is 6mph and tbh we don't even do that much probably 90% of the the time we're probably going 3 or 4 so I should be happy with what I've got and enjoy it.
Thanks.

Fenlander · 23 July 2023, 22:10

Yep I was thinking if you hope to upgrade in the future all funds may be better going towards that and a larger outboard to move it.

Whaleoilbeefhooked · 23 July 2023, 22:11

Looks great..it may be the perspective but is the new prop slightly bigger or not?

Whaleoilbeefhooked · 23 July 2023, 22:21

I hope to get on with the Tobin for now and the next spend will be a 9.9hp next year hopefully! I'm loving it at the moment and hope I keep enjoying it..I'm in my 16th month in remission from a stage 4 diagnosis..I had a tough 6 months chemo and this boat has given me my life back..hence the making memories with my grandson while I still can. Everyone I've spoken to who aren't boat people, remember going out on boats when they were kids..me included..it's such a great way to spend a day!
I'm going to be grateful with what I've got for now ��

Croolis · 24 July 2023, 08:06

Quote:

Originally Posted by Fenlander

Welcome to the forum Nick.

Are these inland non-tidal rivers you will be on? From my experience a 3.5hp motor will push a 3m or so SIB to the max legal/desirable river speed. You are just going to make more wash with a 5/6hp and really need an 8/10hp minimum to get on the plane (with light load) and make a worthwhile speed increase... which of course is only needed at sea.

My 2.5hp on a 3.2m with two grown men on it does 4mph on the Trent upstream, 6mph downstream. Which just so happens is the limit in each direction, I believe.

It's a bit dull, but legal. Also gentle on the young'uns.

Limecc · 24 July 2023, 08:46

Quote:

Originally Posted by Whaleoilbeefhooked

Looks great..it may be the perspective but is the new prop slightly bigger or not?

Same dia. Less pitch.
188×115 vs 188×178mm (rear)

Whaleoilbeefhooked · 24 July 2023, 09:00

Thanks..that's going to the first thing I do ��

Whaleoilbeefhooked · 24 July 2023, 09:03

I suppose it is what it is. It's still a great way to travel.

Limecc · 24 July 2023, 09:14

I've got another alloy prop. Had it in my watch list and the Chinese seller offered it for £13 delivered. Who could refuse?

Whaleoilbeefhooked · 24 July 2023, 09:17

Sounds like my kinda prop! lol was it ok, have you used it?

Limecc · 24 July 2023, 09:33

Quote:

Originally Posted by Whaleoilbeefhooked

Sounds like my kinda prop! lol was it ok, have you used it?

Short shaft doesn't work very well as aux motor because of sea swell. Sucks in air, ventilates and loses grip. Seems very powerful.

Am thinking of buying a small lightweight kayak SIB for it, but also have 100Ah of Lithium & 70lb trolling motor that I'd be tempted to use. Wouldn't compare power-wise but would be silent when out with the group.

leshark · 18 November 2024, 12:54

Quote:

Originally Posted by Limecc

I purchased the readysetboat kit and it didn't get caught by customs. I'm very pleased with it.

Easier to just get a 5hp carb and alloy prop off ebay. Some have fitted 6hp carb and reported it runs too rich. 4,5,6 hp carbs all have the same venturi size, only the jets are different and the sizes are on the parts lists.

The readysetboat prop was actually a lower (and metric) pitch. I expected the reverse. I've precise details if you want them.

I also changed the decals and branding lol

I'd be interested in the spec of the prop? have a Mariner3.5 on a rib and it almost planes, but cavitates before it gets there

User name · 18 November 2024, 15:32

Quote:

Originally Posted by leshark

I'd be interested in the spec of the prop? have a Mariner3.5 on a rib and it almost planes, but cavitates before it gets there

There's an OEM alloy prop available. It doesn't do anything for performance in my experience but it's more durable than the standard plastic one. I wouldn't expect too much from these little motors though.

I wouldn't bother with the 5/6HP carbs either on them. They don't actually make that power, as there's quite a few other differences between the 3.5 and the larger options. The 3.5 is identical to the 2.5 though, with the exception of the bore diameter and jetting of the carb. I'd look for a more powerful motor, or at least try to minimise weight.