Tender Outboard Size. 15HP or 20HP?

[Mango51]

Forgot to answer all question.i Keep engine on the sailboat and rib behind mizzen disinflated. I'll eventually instal davits. Not all sailors do the same things. We can all have opinions on what each individual likes. But their is no wrong or right. I like exploring around my destinations in the tender so doing 12 knots with 4 adults is important for me.

[arsenelupiga]

what about maintenance - can one DIY maintain 4 stroke ?

2 stroke cheaper to maintain ?

[Mango51]

Originally Posted by arsenelupiga

what about maintenance - can one DIY maintain 4 stroke ?

2 stroke cheaper to maintain ?

It would be no more difficult then a generator. Only your sitting on deck with a breeze and a drink of your choice.
2 stroke just lower unit ,filters and 656.

[contrail]

I agree that the prop is a very important part of the equation, more than I had realized. I have a 12 foot RIB with a 25 HP two stroke, and I could get up on a plane but with no more than two aboard. I bashed up the prop and looked for a replacement. The guy at the store didn't have my "size" but had something with a much finer pitch that he said would do better. I took it and can now easily plane with four! So, maybe consider your prop options with an expert, before you decide on an engine.

[YPSILANTI]

Contrail, You make a valid point. Do you recall what your pitch was before you replaced the prop and what pitch you replaced it with. I had a similar experience with my surf launch fishing boat powered with 2 x 50 HP motors. We launch from the beach through very large surf and being on the plane is essential. My desire is to have the same ability to plane with my tender as it will be used in similar launches and for skiing occasionally.

Thanks Mango for your replies. It seems that you're ok with the weight of the 25 hp which is encouraging. A 4 stroke will be much harder to get on the plane but of course offers other advantages. I will stay with 2 stroke. The replies are appreciated and helpful. Thank you.

[Kashmir cat]

My wife and I had a 15hp 2stroke on a 11.5 foot aluminum RIB we used while cruising years ago on our monohull. It was light weight and performed well except it had one major drawback: It couldn't plane up 4 people. So when we had guests aboard or met new people it limited our dinghy cruising range.
Now we have a Yamaha 25 hp 2stroke on a 11.5 aluminum RIB and it planes up 4 people and 3 dogs with power to spare. We don't leave the 25 on the dinghy while on the davits under way. Although the davits are more than rated for the weight, we are somewhat concerned about the extra weight in rough seas. Instead we leave a Yamaha 8hp 2 stroke on the dinghy for quick deployment and overnight stops. If we find ourselves at anchor for more than a few days, we will go ahead and swap out the 8 for the 25 so we can do some serious exploring. Also having an extra outboard as a backup isn't a bad idea.

[YPSILANTI]

Thanks Kashmir, your reply is useful. Is the extra weight an issue or not? If you were to replace the motor tomorrow, would you still go for the heavier 25HP or would you consider a lighter 20HP? Likewise, being able to plane is important for me, I just need to get the three dogs too. LOL.

[Dave_S]

Originally Posted by Navicula

but how does the 20 and the 15 compare when you have 4 adults in it with grocerys and a jug of water??

I also need to make a decision like the original poster

4 adults + groceries = neither would plane. I do think the 20 has a taller pitch and could do with a different prop and that would help. When ferrying groceries only and the weight up front it got up quite easily.

The pipe I fit on the tiller to get my weight further forwards works for the 15 but is too short for the 20 meaning in their current configuration the 15 has more punch to get on the plane. Whether that is weight, HP, or pitch I'm not sure but I suspect all 3 are responsible.

[Kashmir cat]

I think the weight difference between the Yamaha 25hp 2 stroke and say a Honda 20hp 4 stroke is around 15 pounds. So fairly insignificant (about 2 gallons of gas or a small terrier). Now the 25 or 30hp 4 strokes are a different matter altogether. They weigh a lot more. I'd be less inclined to mess around with them.

I don't know much about the 20, but the 25 can plane up 4 people easily in rough seas where you have to throttle up in a wave trough to keep from bogging down and throttle down on a wave crest to keep from going airborne. Lots of power and rapid throttle response is crucial in that situation to keep planed up and comfortable.

As far as weight goes, they both have to be craned onto the dingy anyway, so I'd go with more hp. As far as beaching a dingy, I rarely do it because its too hard to un-beach it! In the Bahamas or Caribbean, I just kiss the beach to unload passengers and dogs, then I throw an anchor out so it floats just offshore. In the Pacific NW where beaches are more rocky and tidal changes are huge, I use dingy wheels. In both cases, weight of the dingy doesn't matter much.

[malbert73]

The prop discussion is a good one. I think most folks would be happier with a more finely pitched prop. Who really needs 30 knot top end speed if that requires displacement mode at 6-7 knots when loaded down. Id much rather top out at 15-20 knots and be able to plane under load.
We usually cruise with a rigid dinghy so a moot point, but with a more finely pitched prop on my 6hp merc my air bottom inflatable will plane with me and my 2 kids (270 total lbs passenger weight)while with original prop no chance.

[a64pilot]

Remember too that it takes about 1min to change a prop, one cotter pin, and one nut. So like our old ski Boat decades ago, you can have a go fast prop for when lightly loaded and you like to cruise on plane at lower RPM and noise, or gear down for when the dink is loaded up but you still want to plane but at a slower speed and higher RPM of course.
Modern four strokes should be rev limited so you really can’t hurt one.

[BlackHeron]

That's a lot of outboard to be hauling around, 15 or 20 IMHO.

We go with just 2hp. It is faster than rowing at least.

[clockwork orange]

As a guy who has always had hard dinghies with oars and a tiny outboard i have always wondered what folks with large RIBs with large motors with a combined weight of 300 - 400 lbs do when you get to a beach in an area where the difference between high and low tide could be a half mile hump. What happens when you come to the beach at high tide and when you get back to the dinghy after being ashore for some hours you have to get it back to the water? Or you hit the beach at low tide and the dinghy is too heavy to pull up the beach do you just anchor it and swim for it when you get back? These are mysteries to me as ive not cruised in areas to witness the solutions first hand. Obviously less of an issue in the lakes with no tides to deal with. I have seen talk of beach wheels but all ive seen are ones that mount to the transom which would negate the weight of the motor but it seems to me you still have to be lifting the weight of the boat and anything in it when dragging it from the bow. This could still be 150 lbs or more. What am I missing here? We just shipped a customers 36ft powerboat to Florida last week that they will be cruising the Bahamas with. They previously had a sailboat in the Bahamas for a few years and this time they took the smallest of the AB aluminum RIBs with an 8hp Yamaha 2 stroke which is a very light combo, because she can drag it up the beach alone.

Steve.

[BlackHeron]

I guess it is all about getting from the boat to the grocery store or the margaritaville bar on plane at 15kt+. People are in such a hurry today. Mo motah!

[Kashmir cat]

Regarding the dingy wheels, I think they are the only way to go when cruising in areas of large tidal changes. In the PNW the tide changes are commonly 10 feet with extremes to over 16 feet. They add very little weight (about 10 pounds) to the dingy and can be removed entirely and again installed in about 30 seconds by simply pulling out cotter pins. Not only do they keep you from being stranded at low tide, they also keep the bottom of the dingy from getting scratched up or punctured by rocky shores.
Normally, they are rotated in the up position when cruising, but when rotated down, they have the added advantage of protecting the prop when exploring shallow, murky waters. There have been many times when I've been motoring along at 5 or 6 knots with the wheels down and find myself rolling up and over a shallow reef like an amphibious vehicle. Very cool.