18' Lund with 90 HP Yamaha???

[Starman]

I'm looking at a 18' Lund with a 90 HP Yamaha 4 stroke. The owner says it will do 35 with two people. Seems a 90 is two small for this boat. I like the boat, but not sure about the 90 Yamaha. Would like to have a boat that would run closer to 40 at Wot. Could putting another prop on it get the top speed to 40?

 

[MT Bob]

Re: 18' Lund with 90 HP Yamaha???

I have a 1700 Fisherman with a 115 Merc. With 2 people it will top out at about 38-40 MPH with full tank of gas & fishing equipment. I mostly run it at about 75% throttle and cruise at around 30 MPH to conserve fuel.
I'd say the 90 HP on an 18 ft. boat is a bit under powered. Changing the prop may help, but I'd try it first.

 

[ziemann]

Re: 18' Lund with 90 HP Yamaha???

When you prop an outboard, your goal is to keep the engine within the center of it's peak power band (i.e. recommended peak RPM). You can fine tune your prop & pitch to gain your peak RPM and may be able to fine tune by experimenting with different props, engine height, and proper trim to pull every last ounce of performance out of that motor. Maybe, just maybe, you can get close to 40...but I seriously doubt it....

I have run 2 different motors on Lund Mr. Pike 17's. That boat is a 93" beam and 17' 2" long. With 32 gallons of fuel on board:

2005 Johnson 90 (2 stroke 60 degree looper)- I was able to get 37.8 MPH with average load and weight distribution in the second hole. I was running a Solace aluminum 13.5x15 prop @ 5700 RPM's. That particular Johnson was known as a real power house for a 2 stroke because if was a V-4.

2008 Evinrude 90 E-tec- I am able to get 34.8 MPH with average load and weight distribution also in the second hole. I am running a BRP aluminum 13.5x15 prop @ 5300 RPM's.

My point is that you have a bit bigger boat and a 4 stroke that will probably provide similar performance to my outboards. I think you are going to be hard pressed to hit 40 MPH. Maybe with a good stainless prop.....

 

[cranksbait]

Re: 18' Lund with 90 HP Yamaha???

Depending on what boat you have that could very well be the proper engine size. Especially if it is a tiller model. If you are able to get 35 with two people, you should be able to get close to the 40 mark solo. I know I lost 5 mph when I repropped but now I am running the right rpm and will make my motor last longer.

 

[ut84088]

Re: 18' Lund with 90 HP Yamaha???

35-38 seems about right to me. I have a 17 foot Explorer with a 75HP ficht and I can get 32-34 at 5200-5400 RPM with 2-4 people. I've thought about going to the 90hp for a slightly better hole shot, but I think I would only gain a few mph.

 

[JJS1]

Re: 18' Lund with 90 HP Yamaha???

I have a 17' (17', 3") 1775 Classic Sport with a 90 Merc 4-stroke and it quickly gets up to 38, 39 - I'm still breaking it in and have only opened it up in short bursts so I'm not sure if that's all it'll do or not, but I'd say it's just about max'd out at that speed.

 

[Woodrow246]

Re: 18' Lund with 90 HP Yamaha???

3 guys all the gear for saltwater crab pots etc....i can maintain 35 if the water is right the fine tuning the trim has a large impact on top speed as well. My 80hp Yammy pushes the boat well and is great on fuel. I would love a 115, but couldnt be happier with my setup for mileage/power.