Zodiac Pro 420 planing and porpoising

[Jnearen]

Picked up a used 420/50hp Yamaha. It stands up on its tail when trying to plane. Only way to make a smooth plane is just WOT it. Once up on plane, at anything less than a fast pace, it tends to porpoise (or buck).

Q1--Are there any trim tabs that will fit it? Bennett SLA6 will not.
Any other suggestions to address these two issues?

Q2--Finally, does anyone make a bimini for these small Zodiacs? A custom is quite expensive. Thanks Jim

[beamishken]

Originally Posted by Jnearen

Picked up a used 420/50hp Yamaha. It stands up on its tail when trying to plane. Only way to make a smooth plane is just WOT it. Once up on plane, at anything less than a fast pace, it tends to porpoise (or buck).

Q1--Are there any trim tabs that will fit it? Bennett SLA6 will not.
Any other suggestions to address these two issues?

Q2--Finally, does anyone make a bimini for these small Zodiacs? A custom is quite expensive. Thanks Jim

Doel fins or similar hydro foils & possibly lifting the engine up the transom would probably help

[Pikey Dave]

Originally Posted by Jnearen

Picked up a used 420/50hp Yamaha. It stands up on its tail when trying to plane. Only way to make a smooth plane is just WOT it. Once up on plane, at anything less than a fast pace, it tends to porpoise (or buck).

Q1--Are there any trim tabs that will fit it? Bennett SLA6 will not.
Any other suggestions to address these two issues?

Q2--Finally, does anyone make a bimini for these small Zodiacs? A custom is quite expensive. Thanks Jim

lift the engine & get some weight forward. Does the porpoising stop or ease if you trim the engine up?

[jonp]

Ive used Bennetts slt trim tabs on many boats and found they worked as advertised with the exceptions of being on a zodiac 550 pro. I wouldn't use trim tabs on these small boats.

Is there an issue with your engine trim that it won't trim down enough ? Can you post an image from the side view with your engine trimmed fully in.

I don't like any of the fins which attach to outboards and have found they can makes some boats dangerous in big seas and side on swell.

Four blade propellers will greatly reduce porpoising effects, help with stern lift and bow down. Engine mounting height can also help with trim issues, where dropping the engine on the mount bolts can improve handling. Often though engines are mounted to low, causing more drag and reduced performance.

There are several reasons that may be causing the problem and several options to fix. Even a transom wedge between the hull and outboard might be an option but without seeing the engine fully trimmed in, it can be just guess work.

Is it an old two stroke or 4 stroke. Does it have the bar lock on the engine stooping the engine trim fully in. Does it even have electric trim, is it tiller or centre console ?

Yes Bimini's are available for ribs, not something I would consider though. Look here and you can see a rib for sale with a small Bimini fitted https://www.boatsales.com.au/boats/d...13862007/?Cr=0

[jeffstevens763@g]

Your too light forward allowing the bow to lift fill a large container with water empty it in stages until you get the right balance,weigh it and replace with useful gear fuel tank etc also check your trim

[jonp]

Originally Posted by jeffstevens763@g

Your too light forward allowing the bow to lift fill a large container with water empty it in stages until you get the right balance,weigh it and replace with useful gear fuel tank etc also check your trim

Disagree, these boats should perform correctly without having to add weight.

[beamishken]

Originally Posted by jonp

Disagree, these boats should perform correctly without having to add weight.

Short boats with heavy engines are prone to porpoising due to lack of lift at the stern, moving weight forward as jeff suggests can often help as will adding lift at the stern, trim tabs aren't realy practical on such small boats which is where hydrofoils come into their own, the folk that find them dangerous or unstable have probably had them on engines far too deep where they can induce poor handling but if the engine is high enough they can solve this problem if moving gear around doesnt work. I think Jeff's suggestion of adding ballast was only meant as a temporary measure to determine how much & which weighty items to move forward.

[jeffstevens763@g]

Porpoising is normally a result of wrong weight distribution. A boat will begin to porpoise badly if it is too heavy in the stern. Adding some temporary weight to the bow and doing a test run will quickly reveal if weight distribution is the culprit for your boat porpoising.19 Aug 2024
https://www.epropulsion.com
Boat Porpoising: Meaning, Causes & Easiest Fixes
Above off google as another opinion than mine

[jonp]

Originally Posted by beamishken

Short boats with heavy engines are prone to porpoising due to lack of lift at the stern, moving weight forward as jeff suggests can often help as will adding lift at the stern, trim tabs aren't realy practical on such small boats which is where hydrofoils come into their own, the folk that find them dangerous or unstable have probably had them on engines far too deep where they can induce poor handling but if the engine is high enough they can solve this problem if moving gear around doesnt work. I think Jeff's suggestion of adding ballast was only meant as a temporary measure to determine how much & which weighty items to move forward.

I have almost 200kg of engine on the back of my 14,6 boat, don't need any weight put up the front. All the corrections in keeping the bow down are from the transom and engine. If the engine isn't trimming fully in enough engine wedges can be used. If the boat is porpoising and lacking stern lift, a decent 4 blade propeller will normally fix the issue.

On our 4.6m long Zodiac we have a Mercury 60 4 stroke. Even with one person behind the wheel and two adults behind the leaning post where the battery is mounted we don't need weight at the front. The boat takes off with a level attitude with no porpoising, cavitation in hard turns with the trim set around 50%. We don't have trim tabs, 4 blade, wedges or foils on the engine.

A manufacturer wouldn't be getting away with building boats where the recommended hp range is causing adverse cruising situations. It's all to do with how the engine is setup. Engine mounting height and prop selection would be my starting point as it sounds like this boat is setup badly.

But hey we will have to agree to disagree.

[jeffstevens763@g]

since you say it stands on end prop choice might be a problem too which also can cause porpoising

[beamishken]

Originally Posted by jonp

I have almost 200kg of engine on the back of my 14,6 boat, don't need any weight put up the front. All the corrections in keeping the bow down are from the transom and engine. If the engine isn't trimming fully in enough engine wedges can be used. If the boat is porpoising and lacking stern lift, a decent 4 blade propeller will normally fix the issue.

On our 4.6m long Zodiac we have a Mercury 60 4 stroke. Even with one person behind the wheel and two adults behind the leaning post where the battery is mounted we don't need weight at the front. The boat takes off with a level attitude with no porpoising, cavitation in hard turns with the trim set around 50%. We don't have trim tabs, 4 blade, wedges or foils on the engine.

A manufacturer wouldn't be getting away with building boats where the recommended hp range is causing adverse cruising situations. It's all to do with how the engine is setup. Engine mounting height and prop selection would be my starting point as it sounds like this boat is setup badly.

But hey we will have to agree to disagree.

I think you'll find many mass produced boats like the ops boat which are available with different power packages are a compromise & require some tweaking to get them right, engine height & trim alone aren't enough to get every boat to ride right with every power option. If that were the case no one would fit trim tabs or stern or bow lifting props.

The op is asking for advice for how to improve his performance, hes had several suggestions all of which can or will help him improve his experience, you nitpicking at folks advice because it doesnt suit your boat isn't realy helpful.

Moving weight about is far cheaper than buying props to experiment with & possibly easier than playing with the height setting on his engine, presumably he will have already played with trim. Cheaper & easier mods would be my first port of call before I start with more difficult/ expensive options .

[jonp]

Originally Posted by beamishken

I think you'll find many mass produced boats like the ops boat which are available with different power packages are a compromise & require some tweaking to get them right, engine height & trim alone aren't enough to get every boat to ride right with every power option. If that were the case no one would fit trim tabs or stern or bow lifting props.

The op is asking for advice for how to improve his performance, hes had several suggestions all of which can or will help him improve his experience, you nitpicking at folks advice because it doesnt suit your boat isn't realy helpful.

Moving weight about is far cheaper than buying props to experiment with & possibly easier than playing with the height setting on his engine, presumably he will have already played with trim. Cheaper & easier mods would be my first port of call before I start with more difficult/ expensive options .

Its not nit picking, its speaking from owning small boats with heavy loads in the rear. The 6m work boat we use carries up to 1.5tons of shellfish and is powered by a 225 and no trim tabs needed as it's a well designed boat.

This boat in question isn't an unusual rare badly built boat and the issue sounds quite extreme.

Yes moving weight may help but it isn't the solution to fixing an issue, it's simply a band aid covering a problem. Having to add additional weight is not the solution either, as this will reduce performance and economy long term, not to mention take up space in the boat.

The solution is on the transom, plain and simple. Either or a combination of prop, trim or mounting height. Yes large heavy non ribs will often need trim tabs due to boat design, however this is a small inflatable commonly used around the world with both lighter and heavy engines on the transom.

If the person who started the post was to ask what mounting height people with the same engined are using or perhaps contact Zodiac, then one thing could be ticked off the list.

If the mechanic who services the engine could check the engine is indeed trimming fully in, another ticked off the list.

If those with the same engine could state what prop they are using or anyone willing to lend a prop to test, then another tick could be removed from the list.

I have around 10 spare props for the 70-130hp range which I happily lend to people testing their outfits, but to be honest I can normally point them to the correct prop from issues they are normally having. This boat in question sounds to be having extreme issues.

A photo with the engine fully trimmed in would help, as would a picture from the line of sight along the bottom of the boat when the engine is trimmed level.

Just trying to offer real fixes to a badly setup boat. When it comes to selling the boat some people might be put off having to load weight upfront and would prefer one how they should perform.