Zodiak MK5 -- motor minimum HP

[Right Turn Clyde]

I am looking at an MK5 (19') to alternately haul a) my spouse and myself with a bunch of camping gear + a couple SUP's or sea kayaks and b) occasionally day cruise with our married kiddos and the g-kids (8 adults).

I've read all I could find here and elsewhere, and for the MK5 I'm not sure if the speed tubes let you run a 60hp motor. Will it plane with a 60 in scenario a)? b)?

Likewise, will it be a slug compared to a more lively 90 or (max) 115?

I realize this is a rare boat, and so not tons of experience. Also should note that we anticipate use being large lakes, and some rivers.

TIA,
RTC

[Peter_C]

Are you talking about the one in Antioch with a deflated tube and a ridiculous amount of patches? With one tube still being deflated?

Either way once you go that big I would get a RIB or hard boat.

[Right Turn Clyde]

That's all fine, but doesn't answer the question. I was hoping for some real world experience with how a 60hp 4st will push a MK5 (assuming it has fully inflated tubes ). I'm actively shopping for a motor.

And while I hope to have a RIB someday, it's not happening now. I also don't want a rigid hull.

Many of the videos I see of the MK5 appear to have either single 40 or 60hp outboards. That seems like a big step down from a 90 or the max 115. So while I'll be lightly loaded compared to the boat's capacity, I am still curious if a modern 60 will move it along in spirited fashion (25 knots) when not facing a current.

s

[spartacus]

The MK5 is a big old bus, with aluminium floorboards. Minus engine, fuel or payload you’re still looking at 250kg (550lbs) alone so you’re not hauling this up beaches like a conventional SIB. This is launch and recover set up on a purpose built trailer, and you can probably add in a transom saver which are common state-side to support the outboard.

Once the boat is built, floorboards in, then you’re looking at the engine to be mounted. The recommended engine is 90hp, maximum transom weight of 165kg (363lbs), this would be bolted on, tiller steer.

Probably the only time you would periodically strip down would be to clean, as sand can get under the floorboards and it acts like an abrasive against the tube material.

So in answer to your question, a modern 4 stroke 60hp will move it with 2 adults on board, but then you are adding in fuel, camping gear, water, food and sea kayaks, so don’t expect it to behave the way you want, if the weather changes and you need extra grunt in a prevailing wind.

Once you have 8 adults on board, then you’re adding 1000lbs. The key here is to get the boat on the plane and allow the speed tubes to do their job, which is effectively lifting the boat out of the water to reduce friction.

I suppose like everything, then 100hp would be ideal.

[Right Turn Clyde]

Originally Posted by spartacus

The MK5 is a big old bus, with aluminium floorboards. Minus engine, fuel or payload you’re still looking at 250kg (550lbs) alone so you’re not hauling this up beaches like a conventional SIB. This is launch and recover set up on a purpose built trailer, and you can probably add in a transom saver which are common state-side to support the outboard.

Once the boat is built, floorboards in, then you’re looking at the engine to be mounted. The recommended engine is 90hp, maximum transom weight of 165kg (363lbs), this would be bolted on, tiller steer.

Probably the only time you would periodically strip down would be to clean, as sand can get under the floorboards and it acts like an abrasive against the tube material.

So in answer to your question, a modern 4 stroke 60hp will move it with 2 adults on board, but then you are adding in fuel, camping gear, water, food and sea kayaks, so don’t expect it to behave the way you want, if the weather changes and you need extra grunt in a prevailing wind.

Once you have 8 adults on board, then you’re adding 1000lbs. The key here is to get the boat on the plane and allow the speed tubes to do their job, which is effectively lifting the boat out of the water to reduce friction.

I suppose like everything, then 100hp would be ideal.

Thanks, spartacus. The relative "stickiness" of all that rubber on the surface is hard for me to gauge. The whole logistics of scaling up I have figured on.

The large group scenario is a once per yr kind of occurrence, so I am not too concerned about that. In effect, hitting 15knots is more what I envision then for an hour of riding about.

Conversely, when two up I am envisioning mounting one of our whitewater raft frames (e.g., NRS Bighorn II) to the boat to provide structure for cooler, dryboxes and seats. Less bouncing on the alum decking that way, too.

What led me to wondering about the 60hp is how many images show 50-70hp singles mounted on the MK5. I suppose all of this is speculation, and there are so few owners of this model that it's tough to get first-hand experience.

From calculations, we would be at 2300lb fully loaded (including boat + motor) for a camping trip. Using a 1hp/40lb ratio we'd need ~55hp. Using a 1hp/30lb ratio, we would need a 75hp motor. These ratios were IIRC from rigid hull boats, so they may not be appropriate.

However, if you use Zodiac's max weight of this model, and divide by the recommended and max hp, it yields either 1hp/52lb, or 1hp/67lb. This is why I am struggling a bit.

It will be interesting to see how much the length of the boat makes it resist rising to plane. Sort of a limp noodle effect. Hopefully that's not the case.

[spartacus]

The majority of these boats are bought by local government agencies, military, commercial such as harbour support and cruise ships (adventure and sight seeing) from new, so are spec’d accordingly, and of course Zodiac will be pretty good at supporting based on order size and intended purpose. If you already have the boat, and have a main outboard dealer near you, then actively seek them out for their input. Most modern 4-stroke outboards are technologically advanced bits of kit, but you can’t invent horses if propped well if you lack overall grunt based on weight. If you’re buying second hand, then start looking for videos of the engine on boats other than Zodiacs. I know a 90-100hp outboard with a tiller arm seems crazy, but it’s a big boat and with kit on board you’ll be glad to have the reserve, even if you don’t necessarily use it all the time.

If you don’t fancy tiller, then I’ve seen these boats converted with seat pods and remote steering. Distribution of weight is important.

[Right Turn Clyde]

I got curious about some of the HP/weight ratios I have seen quoted, and created an Excel spreadsheet to sus out what's what.

Here are some interesting takeaways for OE recommended hp of motors given their spec'd load capacity + max motor weight + boat weight. This is a range of SIBs, including the little Avon 3.15 we have:

MK5
Max 115hp=
1hp/56lb

Rec'd 90hp=
1hp/72lb

Achilles SG-156
Max 55hp=
1hp/29lb

Rec'd 30hp=
1hp/37lb

Zodiac MK2 C
Max 30hp=
1hp/64lb

Rec'd 25hp=
1hp/77lb

Avon 3.15
Max 10hp=
1hp/103lb (!!!)

Rec'd hp N/A

These are interesting ratios when you start looking at them. I'm not sure what to make of them, as there's not a clear pattern. I can say that having tried to camp using the Avon w/ a 9.8 Tohatsu, we were roughly at a 1hp/73lb ratio. It was less than ideal, but got us by for a 10mi one way excursion to test the idea.

[SoCal Hurricane]

The MK5 and FC580 are the same boat. The difference is some extra Hypalon, D-rings, etc…

This boat is used by various military/govt entities but is loved by the Navy EOD community. This boat runs VERY well with the Evinrude 55 MFE. I’d stay away from the engine in your situation, but the point here is that a 60hp Tohatsu, Yamaha, etc (4stroke) outboard will be just fine.

6-8 dudes with dive gear and so forth works just fine. 25knts on a river that isn’t churning like a washing machine will be just fine.

When looking for an outboard make sure to spec the bracket that clamps down to the transom rather than the standard bolt on one. It is an option and some dealers don’t even know that. They are heavy outboards even at 60hp so be sure to have a plan to rig the boat…

Shoot me a PM and I’ll share some video if I can dig it up of the MK5 with the 55mfe on it.

Hope this helps…

[Right Turn Clyde]

Originally Posted by SoCal Hurricane

The MK5 and FC580 are the same boat. The difference is some extra Hypalon, D-rings, etc…

This boat is used by various military/govt entities but is loved by the Navy EOD community. This boat runs VERY well with the Evinrude 55 MFE. I’d stay away from the engine in your situation, but the point here is that a 60hp Tohatsu, Yamaha, etc (4stroke) outboard will be just fine.

6-8 dudes with dive gear and so forth works just fine. 25knts on a river that isn’t churning like a washing machine will be just fine.

When looking for an outboard make sure to spec the bracket that clamps down to the transom rather than the standard bolt on one. It is an option and some dealers don’t even know that. They are heavy outboards even at 60hp so be sure to have a plan to rig the boat…

Shoot me a PM and I’ll share some video if I can dig it up of the MK5 with the 55mfe on it.

Hope this helps…

Very helpful. Thank you. This is just what I was trying to gauge, so I appreciate the scenarios described.

I did just speak with a Tohatsu dealer who denied a clamp option on the 60hp.

That MFE seems like a really fascinating derivation of the E-tech.

[SoCal Hurricane]

Got your PM - I’ll reach out via text shortly.

Regarding the clamp… it’s an option. I’ll have to ask my Tohatsu rep for the part #. Raider outboard is the new vendor for the US military as well as NATO countries. The Raider outboard is a modified Tohatsu (drains like the Evinrude/Johnson) and it has the clamp bracket. It is an option…

[Right Turn Clyde]

Originally Posted by SoCal Hurricane

Got your PM - I’ll reach out via text shortly.

Regarding the clamp… it’s an option. I’ll have to ask my Tohatsu rep for the part #. Raider outboard is the new vendor for the US military as well as NATO countries. The Raider outboard is a modified Tohatsu (drains like the Evinrude/Johnson) and it has the clamp bracket. It is an option…

I think I read that in an article about Raider. Ironically I have now found 4 MFE motors of various eras for sale. But, opting for simple performance, I pulled the trigger on a tiller 60hp Tohatsu today. Painful, but hopefully only once...

[Right Turn Clyde]

Originally Posted by SoCal Hurricane

The MK5 and FC580 are the same boat. The difference is some extra Hypalon, D-rings, etc…

This boat is used by various military/govt entities but is loved by the Navy EOD community. This boat runs VERY well with the Evinrude 55 MFE. I’d stay away from the engine in your situation, but the point here is that a 60hp Tohatsu, Yamaha, etc (4stroke) outboard will be just fine.

6-8 dudes with dive gear and so forth works just fine. 25knts on a river that isn’t churning like a washing machine will be just fine.

When looking for an outboard make sure to spec the bracket that clamps down to the transom rather than the standard bolt on one. It is an option and some dealers don’t even know that. They are heavy outboards even at 60hp so be sure to have a plan to rig the boat…

Shoot me a PM and I’ll share some video if I can dig it up of the MK5 with the 55mfe on it.

Hope this helps…

PM sent. No reply found...

[chris.miller]

Gets to about 20 knots which is about as fast as it should be, with a couple divers or a load of lobster traps. A 60 tiller is fine. Mine is a Tohatsu 40 TLDI.
Avon 5.25

Chris